Hmm... Well, having a devious, mischivios mind does help in matters such as this but, even if you pull it off they will eventually catch on to your fetish however let me see here...a friend of mine tried something like this one summer with a girl at a pool only there was no tickling just massaging. It seems like they were playing tag or racing or something... Anyway the winner got to massage the loser's foot which stupedly was a dead give away -he may as well have wrote foot fetishist on his forehead, the idiot! Let's try something with a bit more imagination that isn't so obvious, shall we? Maybe a game with the classic interrogation of captured prisoners or a game like truth or dare with a tickle-twist to insure that those feet always end up in your hands. Maybe the truth question could be "things that you hate" or "worst sensations". Maybe you could gather info this way and then go with a question that they don't want to answer then follow it with a harsh dare that they may back out of which results in a penalty/punishment. You following me so far? Maybe even try a game based on enduring specific sensations or keeping a straight face during tickling. The human imagination can be unlimited. Just sit around and think up stuff, ponder it a bit and then give it a try! Good luck!
-TK
