We raised the outer track, by using the 2"X1" wood pieces.
We cut them to the size needed (subtracting the thickness of the masonry board) and placed them approx. every 5 to 10 inches.
We used liquid nail on both sides and put one screw from under the board to hold into place. Than we laid the masonry piece that we cut into shape on top of those raisers.
Don't worry about the little space between th raisers and the masonry board, the liquid nail will fill these.