it's all in how you configure your destination codes. If you break 911 and 9911 in your destination codes, then you can build other destination codes (9A, 99A, 91A) to route other 9+ traffic over the IP trunks and out the main office. You'll need to configure the NRS to allow this as well as configure some other dialing plan info on the SRG.
So yes, it can be done.