Couldn't you just make some missions that let the player go up without a specified flight path and just hunt around for some enemies?
Umm, maybe I'm missing something, but can't you just go off on your own anyways? I use to wander from the set flight path (within reason) with the earlier version of PW's missions, and yes, enjoyed doing so very much.
With RL in the way I haven't gotten to fly much lately, so haven't tried wandering with Pat's latest version, which relies on 'moving AI flight triggers'. Maybe going off the set path now results in no action???