You don't have to desolder the ribbon cable. You could use some sort of ribbon cable connector, if you have one available. But I found it more practical to only have the wires I needed. And desoldering the ribbon cable was fairly straightforward.
The piantor looks like a nice piece of kit! Unfortunately the PCB doesn't seem to have any holes to accommodate a trackpoint. There even seems to be a trace right between the YUHJ keys, so drilling a hole is not possible either.
I'm using the thumb cluster keys.