Without the grid tie, I suspect getting the rebate will be very hard.
If all of the loads are on a sub panel fed by a transfer switch, connect the grid tie inverter to the sub panel. When the PoCo goes away the inverter continues to feed the sub panel.
You will just figure out a way to get the inverter to supply the load with no utility present. Perhaps some sort of contact on the transfer switch to prove no utility connection?
