If I understand, you want to add the trackball to your existing control panel, without "making a hole" for it, basically you want to just stick it on top of the existing control panel.
IMHO, I wouldn't bother dying the trackball. It's going to look "added on" no matter if you dye it or not.
This is a lot of work, and is just the way I would handle it but....I would cut a new control panel (with room for the trackball), and re-mount the existing controls on the new panel (Obviously a problem if you have artwork/plexi that you don't want to mess up.)
Maybe make a second control panel, with trackball, spinner (maybe a steering wheel), and just swap the 2 panels back and forth depending on your needs. It helps to have extra room when using the trackball, and a 2nd panel, would give you plenty of space.
I'm not saying you shouldn't "add-on" a trackball, I just think you would be wasting your time trying to make it look good. If concerned about looks, rebuild....just my opinion.
Good luck either way!