home-made ice tires are pretty common in mountain biking too. Typicallly they do the same thing, get some short wood screws and screw them through the knobbies from the inside out, cut the tips off (although you probably don't need to with an RC vehicle, thats mroe for safety) and then cover the screws (on the inside) with several layers of duct tape. I think if you do it with a foam insert thats as hard as possible, you might be ok. (as far as the screws not coming back out), but the best way is to get some that have nice thick knobs, and then screw through the knobs so the threads bite and it doesn't want to just push right back in.