Play any champion In custom games

I think that riot should make people able to practice champions in custom game mode even if you don't own them. They could even limit it to a few games on the champion so that the player could see if they like playing them or if they want to buy the champion. I think this would really help lower level players find champions that they like to play. I've wanted to buy a few champions but I'm not really sure if I would like them. I know that's what the free to play champions are for but it takes awhile for the Champion you are waiting for to come up.