The only thing I could think of would be something like these
they are sold at dance stores as heel grippers but I you might be able to make some
thats all I could think of hope it helps
payless sells them for $1.50/pair
also if you go into gottschalks if you have one near you (oregon/california/nevada chain) and ask for a pair of heel grips they will give them to you free (i used to work there). i assume most department stores with large shoe departments will do the same but i haven't a clue really.
i had an adorable pair of chunky mary janes that were one size too large as well. i got some of those heel grips and put them in (they seem to decrease a little less than a half-size, maybe like 3/8 of a size) then i stuffed a small amount of fabric into the toes. it's not perfect, but it works :] also the heel grips are stackable, you probably can't stick them more than two or three on top of each other before they start falling off, but i think i have one pair of shoes i wore to work a lot that ended up with three heel grips in the back. i was using the cottony ones though (they don't add quite as much in the back as the rubber ones that are pictured do) and those stick to each other quite well, i don't know how well the rubber ones do.