This can be done, but involves bridging rather than forking. Keep in mind that the AA acts just like the Phone Port in most respects with its own DigitMap and OutboundCallRoute.
When Option 1 is chosen the OBi firmware sends a "0" to the AA Digitmap, which gets passed on to the AA OutboundCallRoute and matches this rule:
{0:ph}
This sends the call to the local Phone Port of OBi 1.
Assuming OBi 2 OBiTALK number is 200123456, then the call can be bridged to OBi 2 using this rule:
Voice Services > Auto Attendant > OutboundCallRoute:
... other rules here},{0:ph,pp(ob200123456)},{... other rules here ...
This sends the call to local Phone Port of OBi 1 and to the OBiTALK Service > InboundCallRoute of OBi 2. If you want the Phone Port of OBi 2 to ring then make sure that this is set:
Voice Services > OBiTALK Service > InboundCallRoute: ph
There may be other "Circle of Trust" rules trying to send an incoming call from OBi 1 to OBi 2's AA. That might get confusing!
If the call is now answered at OBi 2, then the call is bridged from OBi 1 to OBi 2. So some resources are in use in both OBi devices during the call.
You do not say how you do your forking or connecting. The above will work over any distance and uses the Obihai servers to connect the two OBi devices together. If the two OBi devices are in the same router subnet, then I prefer to keep things local and use the ip address / port of the target OBi something like this:
Voice Services > Auto Attendant > OutboundCallRoute:
... other rules here},{0:ph,sp2(201@192.168.1.10:30123)},{... other rules here ...