As Ginnie & Naughtygirl mentioned,cunnilingus(oral sex)is an excellent way to start combining sex and enemas.
A number of years ago, I was involved with a lovely woman who was anally erotic. She enjoyed enemas,labial engorgement,nipple erection,flushing of the skin,gushing and all the other markers of arousal. Yet she kept them completely separate from vaginal sexual activity between us,one then the other, not both at the same time.
Over a period of time,as we started to we started to develop mutual trust in each other and our boundaries,I slowly and unhurriedly brought oral sex and enemas closer and closer with the waiting period between the two shorter. Then, one evening, as we lay there pleasing each other orally with a bag ready and hanging on the stand and the nozzle lubed resting nearby,(willing by previous discussion to stop any time she asked) I reached over and picked up the nozzle and gently and very slowly began to insert it into here rectum. She gave out a deep/low/moaning growl which was felt as an intense audible vibration on my penis, her pelvic motions intensified and began to gush vaginally drenching my tongue and face.
After a period of approximately 15-25 minutes of doing this with the nozzle in yet with the clamp closed, of her own accord, she reached over and opened the cut-off clamp(the other being an adjustable rate of flow set to it's lowest possible rate).
What ensued was a very intense orgasmic response on her behalf as evidenced by her actions and admission, the experience was also pleasurable for me, yet my priority was to give her as much pleasure sexually with an enema as possible.
We continued on with oral sex and enemas not hurrying a progression at all. After close to 10-11 weeks of doing things this way, she one night said she wanted to "ride me first" before doing as we had been. I said ok, we initiated a languid foreplay, when she was ready, I lay back and she straddled me and slid down firmly. Before leaning forward and laying on my chest,she reached over to the prepositioned enema rig
hanging on the stand, grasped the fluted nozzle glistening with lube and slid it deftly deep in her rosebud. She then lay down on top of me and began to rock rhythmically, with me gently responding in kind. As she began to sink into a steadily increasing arousal, she opened the clamp on the hose, water began to slowly and gently seep into her.
As she began to fill and the warmth spread through her, she began to spasm with very intense and ever increasing rectal & vaginal contractions, clamping my my penis in a deliciously ever tightening velvet vise. The flow, set to it's slowest/lowest setting allow the bag to empty in about 35 minutes. We lay there, with legs intensely intertwined, rocking and bucking against each other long after she had taken a full 2 qts of warm water. I reached over and closed the clamp,offered to remove the nozzle and let her get up and release. She raised her head up, and pointedly said "don't you dare" while clamping her cheeks tight to hold the nozzle more snugly & thrusting firmly back down on my penis. We lay there in that embrace passionately snuggling/
nuzzling/caressing and tenderly cradling each other for another 20-35 minute before the urge to release compelled her to get up with great reluctance and go to the bathroom.
From that point until we went our separate ways, enemas and penile/vaginal sex were an integral part of our relationship giving and receiving gently to each other with no struggle for dominance. The point is, if you love your partner and care about her needs and go at in a manner that is attractive to her with options to stop,she will most likely not only like it,but quite possibly intensely desire it.
The next is a side note. Prior to meeting her, I had not been able to easily ejaculate during oral sex(most definitely psychological)as a result of once having been bitten severely @ age 19. One evening, when we were in foreplay preceding enemas and sex, she asked me why it was so difficult for me to cum orally. I told her about what had happened, she said "oh" and said nothing more and we continued as before, with her being a bit more gentle with her mouth on my penis ensuring to cover her teeth more with her lips.
By that point in our relationship I had gotten to trust her that I would never be bitten, and did not fear that happening with her. About a month and a half later, with me receiving as a prelude to some favorite play we had created, I was slowly filling in the simms and she was caressing me tenderly and erotically, which had that evening, gotten me to a particularly intense erection. At a particularly intense point, I was copiously dripping clear pre-cum, when she started to slick & spread it all around the head of my penis, while doing so, she gently tugged at me to roll on to my back. As I turned,in one swift motion, without hesitation,she tenderly engulfed my shaft with her soft lips deeply while simultaneously opening the flow of the enema fully. She made a lollipop of my penis constantly sucking with her lips and no teeth while the warm water flowed across my prostate filling me. My pubic muscles began to twitch involutarily, and I started to ejaculate intensely with complete abandon.
She continued to suck on me while I subsided,milking and swallowing greedily every drop of cum that she could. Never removing her mouth, she continued on pulling me to another erection within less than a minute. Once again erect, she removed her mouth and put herself on top gently stroking up and down, clamping me with her vagina until I came to another quite satisfying orgasm. The point I wish to make is, that, with the simple expedient of mutual respect for the needs of others,many things can be accomplished with respect to enemas and sex. :)