Build 2 system shortcodes:
[9]*72 / Dial / *72 / 0 to forward.
and
[9]*73 / Dial / *73 / 0 to unforward.
The pain of this is that you do not always get Line 1. You may have to dial it a few times to get the main line (not an issue with 2-3 lines). I think this work with 4.0 using ARS, but I have not tested yet.
Good luck,
Frank
Frank Robertshaw
The Phone Guy
Nashville, TN