Hi cacuttie, I'm Mitch. Welcome to the forum. I've had a bit of experience with massaging a girl's feet, and easing into tickling.
Massage can take place in many different ways, and by using different parts of the hands. One can actually use their palm, and rub the foot up and down the sole with the base, or middle of the palm, and even use the fingers a bit to rub the sole. As you are rubbing, you can use like the middle of your fingers, not even the tips, but the middle, to give a slow massage/tickle type motion. This way, it looks as if you are intending to massage his feet, but are also sneaking quick tickles, and tickling motions in there, without it being too obvious. I've done this to a girl, and had it done to me, and it is a good subtle way, I find, of sneaking a tickle in, without looking obvious to the person being massaged/lee.
Hope that helped. Good Luck. Hope we can chat at some point.
Mitch