Try using pizza pans on top of your current hubcaps. I've seen someone on here has them (is it MetroMPG? I'll let you search the website, heh) but here's a quick link I found. They look pretty 'professional' enough to me, smooth and clean.
2004 Prius Custom Hubcaps
I want to try it but my rims don't have hubcaps. (and they're fairly smooth already too) I'm thinking I may just try gluing plastic cut-outs into the holes (like... again, I cannot remember who. I've read so many posts here recently that my head's swimming a bit)