Since the trackball is USB, you might want to consider housing it in its own little external CP. Then you could have a USB port on the front, side or back of your bartop. It is super easy to plug in when you want to use it, but you don't need to to make the CP on the bartop unnecessarily large.
But there a couple of negatives to this option... if the trackball will be lit, you will need to plug/unplug additional wire. Also if there are trackball games with buttons they won't be next to the trackball, unless you add buttons to your mini-trackball CP, which would require an additional wire again. But both the buttons and the lighting could be easily wired to a CAT5, to take advantage of easy connecting.
Just another option to consider...