What the folks at Jetcat told me to do is:

1) Countersink the tapped holes in the Kangaroo, most of the c'sink will be in the gellcoat, screw head should be flush to just below.

2) Make a wood block with the same mounting hole pattern but with minimal clearance for the flat head screws, and countersink them.

3) Place the flat head screws though the mount and into the holes in the block.

4) Place a screwdriver in the screw head and hit it with a hammer. test the fit of the screw to the holes and the extrusion to the Kangroo

this extrudes the mount into the hole. if depth were correct all 4 screws will be just below flush.

Adjustments:
a second hit with the hammer may be needed for deepening the extrusion
countersinking the holes deeper in the wood block & goto step 4
countersinking the holes deeper in the Kangaroo

This process will not reduces the wall thickness of the mount

use new screws for intallation. toss the forming screws away

bob E