Never thought of trying to break off the high spots. My fear would be if the client would like that idea. (After all you are changing the wall permanently.) Also, I think regardless of how careful you are, it's never going to be the same as installing on a true flat wall.
I still say you need to use some kind of raceway top and bottom to tapcon to the wall to create a flat surface to mount to. A treated 2x4 should do the trick and then just screw the poly-metal to the 2x4's. Otherwise you'll have to figure out some kind of shim/blocking to use and because of the irregularity of the wall you're going to be cutting all kinds of different thicknesses....
*BTW - just sent you a friend request.