We have done something similar but the softswitch is Broadworks. We take incoming calls from the FXO and send them out SIP to the softswitch. This way the switch can handle transfers, auto-attendant, and the like. The one-off location is part of the customer dialplan and things will work better that way.
If you want to keep outbound local calls from that branch on the FXO rather than backhauling to your softswitch, there's a trick to do that. operationally there are advantages and disadvantages. Keeping them local reduces traffic on your point-to-point line if it's congested. Pushing everything back through the softswitch is operationally cleaner to troubleshoot. Another advantage to sending all outbound back through your softswitch is that the local telco charges for message units on outbound local analog POTS lines is often substantially more than hauling them over SIP anywhere in the country.
The trick to routing local outbound calls over the FXO is to put the local calling patterns in the TA924e dialplan under the category "Always permitted". This is interpreted by the TA924e the same as 9-1-1 and those calls will be routed out the local FXO at all times. It isn't well documented but it works. Personally I'd send all outbound including local through your softswitch unless the point-to-point circuit is going to be congested. This way the local FXOs are available for incoming calls.