@BigBowMan is exactly right. It really is that easy. I've been meaning to do this on an Axiom, so decided to tonight. Slipped the charger over the stock, turned it upside down, slipped the 2 mounting block halves into place, and traced around the edges of the blocks
Then I removed everything, used a c-clamp to hold the block that has the through-holes (vs the tapped hole block), and drilled the 2 holes through the stock.
Then I simply bolted the block halves on. Charger held in place up against the ramp of the stock like its supposed to be.
This was on an old Exo stock (I'll need a longer rope for it now), but the idea is the same for a Matrix.