Well I tried to get creative...  first I used some random aluminum baking pan thing we had lying around the house, folded it a few times.  It must've either not been thick enough or not cover enough surface area, because although it was better than nothing, the kickstand still sank a little.

Next I just cut a piece of rubber tube (heating tube or something for a car, maybe a couple of inches wide when flattened, 4 inches or so long).  That wasn't hard enough.  I was trying to find something I could easily slip into my pants pocket since I don't have saddlebags and don't wear a riding jacket in this Texas heat.

I was at the dealer the other day getting my bike inspected and asked them about it.  They gave me an orange plastic "Cycle Foot," and that seems to work pretty well.  They didn't charge me anything for it, and it's not too bulky to slip into my pocket, so I think that oughtta do it.

Thanks for all the suggestions.