one of my favorite toys is a inflatable blow up plug, except I have modified it. As other have found they eventually break, so I covered my broken plub with a medium sized latex balloon. first put a little corn starch in the balloon, to use as a dry lubricant that wont break down the latex. I used rubber cement glue to seal it at the reduced diameter section and stretched the balloon right over the base. I then put electrical tape pulled tight around the glued area for extra support (you'll see why later). Use the good/real electrical tape, not the cheep vinyl tape.
I then cover the first balloon with another balloon, putting a little cornstarch inside for lubricant. I continued to do this till I had about 15 balloons on it. It was tricky sometimes getting them over the base without them ripping, but with a little patience and practice it works.
This has two advantages, when the outer balloon breaks down from were and tear you can just peel it off. You can always add more later. the second advantage is that with so many balloons it becomes much stiffer than the original flimsy membrane that was on it and so you can slowly strech your anus by moving it in and out slowly increasing the size as you relax.
hope some of you find this helpfull.