Here's some other ideas: the source of the problem is the tire bead slipping on the rim. Most off road motorcycles have rim locks to prevent this very thing; as Josh said, and old motorcycle trick (before rim locks were standard equipment) was to use short screws thru the rim and into the tire bead. This probably could be done on an aircraft wheel if you don't mind drilling your wheel rims. But I also noticed on my Honda XR500 dirt bike that the inside of the rim where it contacts the tire bead was somewhat serrated to provide a rough surface to prevent slipping under torque. Maybe this could be done to an aircraft rim with a Dremel or something.

On second thought John, I don't think your idea of eliminating the talc would help much, since it would only ensure the tube moves with the tire, which is NOT what you want. You want the tube with its valve stem to stay put exactly where the valve stem hole is in the rim. The only way to do this is to prevent the tire from slipping on the rim. I doubt very much that the small valve stem has enough strength without tearing the rubber to hold itself in place if the tire slips, even if you put massive amounts of talc inside as Josh was wondering.

Bottom line for me would be: no talc or rubber lube on the bead/rim area, roughen up the rim bead area on the wheel, and be reasonable in lowering the inflation pressure too much. As part of my preflight, I always look at the tire valve stems to see if they are starting to tip sideways.