I easily built an electrified clit trode out of a narrow vacuum nipple cylinder and a short piece of Conductive Rubber tube of approx the same diameter as the cylinder. I put it over the end of the cylinder and folded the loose piece of the end of the tubing into the cylinder -- inverting it into the inside of the cylinder. That is, the one piece of CR tubing is put over the open end, with part protruding, which is folded inside, so that you have part of the tubing on the outside (where a gel pad is attached to it for a connection), and then folds into the inside of the same cylinder. Note, since CR does not stretch much at all, you have to get CR tubing just the right diameter. You only need at most 2" of tubing.
It stays on quite well. Even with a slight vacuum (and it SHOULD be ONLY a slight vacuum), it will not come off easily if you put some goey material to make a good seal. I use Spectra 360 electro gel, which extends the electro area a bit more. After a while, the clit expands some into the vacuum cylinder, and if the cylinder is narrow enough, the clit will make a tight fit against the CR which is on the inside surface of the cylinder. Handle the cylinder gently, since once the clit expands to fill the space, it will be a tight fit.
I have only tried it once, when a college coed wrote me online and said she wanted to try this. She liked it so well, she came back monthly until she graduated and left the city. Since it doesn't come off easily, you can keep power on low and run it a long time so she can enjoy the rhythms of the power box for a long time.
The other uni-polar trode can be either a large anal trode, a vaginal one, or a gel pad on the perineum.
Women who like doing this say that the very best feeling in the world results when you pair it with a uni-trode in the urethra -- either touching the bladder sphincter, or pushed into the bladder. You have to be extremely careful to be as absolutely sterile as possible, as this risks a UTI.