Edit: I came across this:
https://deskthority.net/wiki/MX13_SpaceSaver_Keyboard which uses the Trackpoint module from the SpaceSaver II.
Apparently the trackpoint controller is not in the trackpoint module with PS/2 output, but on the main logic board as the keyboard controller ...
but the circuits are separate from the keyboard functionality, with independent power. If there is space inside your build for it, you should be able to include it.
Old: Some Trackpoint modules -- but not all -- talk the PS/2 protocol.
If it speaks PS/2 then you could use it with Hasu's
TMK firmware - it should have support for PS/2 mouse input. I don't know if it is officially supported, however. You might have to do some hacking.