UPDATE : Since posting, updates in OpenScad had revealed a few warnings in the code. I have now resolved those. I have also included the logo batman.stl so it will work with something right out of the box.

If found Thor3D's wheel cap Generator, but I wanted a manufacturer logo and a rounded edge. Now you can add any logo with minimum of effort.

Download or create logo (as STL file) and place it in the same folder as this OpenScad file

Adjust the Cap Parameters so the cap will fit your wheel.

Change the file name for the logo STL file and perform a quick render.

Adjust the X and Y offsets so the that logo is centred, re-quick render after each adjustment to check progress. The offsets will depend on where the origin in the STL file is.

Adjust the scaling until the logo fills the cap, and is raised by the desired amount. Quick render after each adjustment to check progress.

Full render and save as STL file.

I have included a couple of images of caps created with logos found here on thingiverse.