Question, I know it's not as good as a dedicated jig, but if you had the hub and brake, could you just put the hub in the frame/fork and clamp the brake onto the rotor, use that to tack? Maybe small quick tacks so you don't melt anything on the hub or the brake?
I know I did that on a tandem once long ago, like in the '80s, but I don't remember the brake brand or how well that method worked.
I guess if the brake has a piston on one side only*, then you might need to shim the rotor/hub connection while tacking, then take the shims out for use, so the rotor ends up centered between the pads when they're retracted.
* I don't pay attention to disk brakes, are they even made like that anymore? I'm guessing hydro brakes come in from both sides equally.
Mark B