It'd work for a few times, at least. In the 90s, BMW gave out plastic wallet-sized cards with flip-out emergency keys with at least some of their cars. Not super durable for repeated use, but handy to have. Looks like something similar continued into the 2000s for a while, at least: http://www.bimmerboard.com/members/q/original/BMW%20Transpon...

My '96 Chevy Cavalier came with one of those.

For occasional or one time use, that's actually fine. Just need a tension wrench to turn the cylinder so the plastic doesn't bend/break.