I just installed a v3 on a 2004 STi used for hillclimbs, but I made a complete custom harness, and have the cams locked, using the traditional cam trigger instead of the AVCS cam triggers. And the 2004 (at least this one) doesn't have drive by wire.
For the 2007 I believe those have AVCS on the intake and exhaust cam? Messy. You could always swap out the drive by wire throttle body with a conventional throttle body.