Slopes, have you seen TuEr0s' touch switch as yet. It's a piece of solid wire surrounded my an insulator, wired to the Mosfet:
The trick with such a switch is the conductive body. For a touch switch, you need two contact points. In the case of a single point, like in that photo, the body is the second contact. Your finger will touch the body and the other contact to turn the unit on. For a non-tube mod, or any mod where the body isn't the path for the negative, you could use a similar setup, but you'd need a second ring. If you look at the bottom of a 510 atty, it's a perfect example of something you could use. It has a center contact surrounded by an insulating o-ring and then an outer contact. That would make a perfect "single-finger" touch switch.
For a wiring diagram, there is a thread around here somewhere about exactly that. I'd link it, but I'm at work and don't have the link here. In fact, just a week or so ago, I had almost the same discussion and linked the same thread for the same purpose. Maybe check back a couple pages on this forum and see if you find a similar title.