You can assign pool 70 to a "button" on the extension through WinSPM, set it to NO ring, and change the Auto Line Select to grab that first. You also now don't have to dial a 9 to go out.
You could change the FRL of the extension, and build a new route in ARS, with the matching FRL and 70 as the pool dial out code.
You could give the extension Pool Dial Out access to 70, and have it dial 70 instead of 9. Be sure to pause after the 70, to allow the line to connect and receive dial tone.