Personally, I am not a big fan of the Aero wheels without the caps - they look unfinished to me. But that is just my opinion.
HOWEVER, I remember once seeing a center cap that filled in the indented part in the center, including covering the lug nuts. At the time, I didn't capture where they came from and I have been searching in vain ever since to find them. If anyone knows where to find them, let me know - I will be most grateful.
These? Custom Aero Wheels