Hi Roblp,
Try the following on your first OBI:
Voice Services -> SPX Service -> X_InboundCallRoute: {pp(obXXXXXXXXX),ph}
... replacing the red X with whichever SP you are using Google Voice (i.e. SP1, SP2, SP3, or SP4)
... and replacing the green X's with the OBI 209 number of your second OBI unit.
Hope it helps,
pc44