Calling 10 digit extensions using 7 digits

Greetings, I’m looking for a way to set up 10 digit extensions for customers, but yet allow these extensions to connect by entering only the 7 digit number (assuming a local area code). While I can dial the 7 digit number, and the outbound route adds the area code, I’d like to keep those calls inside the local machine, instead of passing them out the outbound route, and then back into the machine.

Any thoughts?