I would advise against it, but at the same time I've heard of people fitting rims that are one size up. Your best bet is to contact your local auto-repair mechanic and see what his opinion is. Odds are, if he's at the desk, he has time to answer your question. That, and he gets PAID to do it, so of course he wants to get paid / answer you.
Personally I've stuck to the correct rim size with my rims on my volvo, I don't trust putting different sizes on.