I have a solution for your problem. I have NOT tested this.
It's a two step process to make the call.
Get a second Sip2Sip account.
Make the account all numeric, so you can call it from a keypad.
Register SP2 on the Second Sip2Sip account.
Change SP2 InboundCallRoute to {(1st_Sip2Sip_acct):aa}
Change Voice Services => Auto Attendant => Primary Line = SP1
From Bria dial the 2nd Sip2Sip account number.
You should get the OBi100 Auto Attendant.
Follow the prompts to dial the number.