I’m not sure if I understand correctly.
The PA34 doesn’t stall, it’s an external program which triggers a false stall message?
No need to calculate CG. Simply move the CG aft until you are actually able to stall the PA34.
(CG would be most likely still approximately in the center of the diagram.)
edit: just re-read your previous post. If takeoff is normal at 4700lbs (flaps 0° 79kts) how can the PA34 stall with full flaps at 80-85kts? Strange indeed.