My son does this perhaps its a julie thing
I usually try and hold his hand, unfortunatly the hand he has under my breast I cannot really control. I have tried pinning it down with my breast but this only works when gravity is really strong that day.
I have tried giving him a taggy to twiddle, a stuffed animal to hold, and tieing his arm down with the blanket just makes him angry.
So holding his hand is all I have come up with. OH also I have sucked his thumb, its totally gross, I know where his hand has been. If I really need my second hand for a moment I will suck his thumb.
Wish I had an answer.
julie