Wardie, this is what I did. Just one possible way.
I originally installed these with the stock exhaust on and since then, have gone to a different single exhaust, but this is what I did to fit the stock one.
I wanted to keep my original rear signals, and also installed an integrated led tail light-brake light assembly. (lots of light now)
I took off the original signal assembly and cut the rubber down so as to shorten the length that it stuck out.
I then plugged the hole that the signal light assembly was mounted in, on the fender with a large flat washer and nut, and painted that washer black so as to hide it a little.
I did do a fender mod to cut back some of that look, but I just attached the bracket that came with the Motech kit onto the rear fender (drill and bolt it to the plastic). I mounted my license plate and that bracket with 2 bolts. I then drilled 2 more holes in the plate and plastic to add 2 more bolts (more stability).
It looks OK, not fantastic, but it is completely functional.
Those mounts are so good that 3 of them (less the rear one we are talking about) will hold that bag on.
With the 4th point (rear bracket reinforced with the second pair of bolts) it is rock solid, and you could lift the bike up by that mount.
Hey good luck brother!