Descibes a mod to the CST2545-5W Trackball to add two switches to the 1.3v PCB. These can be your button 4 and 5 on this trackball.
The popular /u/ripster55 mod describes an earlier PCB with a different location of the extra switch solder pads.
On the v1.3 revision they are located on the right side of the PCB, labled J3, J4.
You will need to drill a hole in the back for the wires to escape the chassis.
Solder the ends of the wires onto the switch you're using. Be careful not to burn the insulation of the wires like I did.
I 3D Printed mine from a file I found on Thingverse by user AnEnemyAnemone (thank you!).
I chose to epoxy my housing directly to the chassis of the trackball as I am incredibly foolhearty.
This post on reddit has photos of a version of this same housing but with a backing that would allow you to use simply double-stick tape. You can find the files for this housing on GrabCAD