Unable to create sip trunk

I’m new to Asterisk and FreePBX. I’ve downloaded Asterisknow 1.7 and I’m trying to follow the steps in the article below to set up a SIP trunk with office communications server. The instructions only cover the CLI, so I’m trying to figure out how to do this via the FreePBX GUI.

I have working extensions - I can make and receive calls from other Asterisk extensions.
My SIP Trunk appears to be correct.
I think I need help with the outbound route.
From the steps in the above link:
exten => _NXXNXXXXXX,1,Set(EXT=+${EXTEN})
exten => _NXXNXXXXXX,n,Busy

Looks like he’s added a “+” to the number dialed which is needed by OCS. Is this possible through the FreePBX GUI?