Contemporary sticks have 4 terminals - see patent drawings for the schematics, but there are 4 resistors in addition to the strain gauges. It is humanly possible to desolder those and have a common ground + strain gauge outputs out, but it involves desoldering 0603 SMD resistors. Which is easy if you have a JBC with tweezers, but otherwise not.
I don't. You seemed to be worrying about GPIO availability.
There are literally 3 pins left unassigned on the kit, despite them not being marked on the "default pinout" picture. It only describes "user-serviceable" pins that are used in default pinout. No markings next to the pin doesn't mean it's unused.
Anyway, if you plan to attend the big meetup - I'll be there, we can chat about that.
Edit: looked into Location field. ^ doesn't seem likely.