I must say that I've never decorated anything
I just make deco sweets out of clay and make jewellery and accessories. But from what I've heard, people are usually piping straight onto piece you are decorating. I don't think anyone is sticking them after they dry. Unless they are buyin already made cream cabochons (usually made from resin). Just remember to first put some protector film or something like that, just in case you wont like the deco or you'd like to change it in the future. You won't destroy your DS then
(search on ebay for them)
Hopefully this help a little, but I hope that someone more experienced will answer your question
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."