Just go get frequent pedicures. As often as you can reasonably afford . . .
Seriously, I've been screwing around on twitter & when I search "ticklish" there are beaucoup tweets from young women saying how badly pedicures tickle. Most hate it but some enjoy it.
Something motorized on a timer that you could turn on but not turn off. Practice self bondage and use something like that. Just don't set the timer too long, or you could be in real trouble! 😛
It should be possible to make one with a robotics kit like Lego Mindstorms or something. I've been wanting to do that for a while. Seems like kind of a sad endeavor, though... probably should spend the time looking for a girlfriend instead. :/