I have a TI ( I don't own a PA) but I use the mirage drive pretty much 100% of the time, even when I'm using my motor, using the mirage drive and the motor together extends your range quite a bit. So I would be lost without my mirage drive, and it would be awkward for me to switch back and forth, you would need to store either the torqeedo, or the mirage drive when not using them, then switch back and forth, etc.
Having the Ultralight 403 Torqeedo motor mounted in the back out of the way of everything else, actually in my opinion would be the better setup, nothing to stow, and nothing to remove. You might be able to rig the steering as well which would help make the PA steer better. I believe the ultralight 403 is very similar in price to the Evolve (they are basically the same unit, but Hobies is modified for Hobie use).
This is what it would look like ( http://www.torqeedo.com/us/electric-out ... and-canoes
Of course this is just my opinion.