I have replaced mine with high quality ones that I bought from the U.K. I don't think they will go over the existing ones, but they look great and fit great!
They're more pricey than some, but the quality is well worth it. Here's a link to where I got them, you'll have to scroll down until you see them, You can choose from the multi colored ones (Limited models), or the black and chrome (base models):
Wheel center cap logos
Here's a link to how I replaced mine:
Wheel center cap replacement