Has anyone tried, or have a method for, installing Kadee 309 Electromagnetic Uncouplers from underneath after track has been laid?

After operating the layout for a while I realized I missed some spots where I want these uncouplers, but I don't want to rip up some of the track and turnouts to do it. I'm afraid I will damage something and then have to spend money on, or not be able to find due to COVID shortages, extra track and turnouts.

I think I can locate the spot for installation below by drilling small pilot holes along the track center line between the ties above. Then carefully drill / chisel away the 1/2" plywood from below with the 1/4" cork roadbed as a buffer from damage. Next I would cut out the cork with a hobby knife, screw the long narrow mounting bracket of the 309 upside down to the electromagnet bracket, and then screw it up into the sub-roaded for a flush to rail tie installation. I might have to chisel out little pockets on either end of the sub-roadbed for the screw tabs on the mounting bracket to get the mounting bracket flush with the ties (the same way you cut out a little area in the road bed when mounting from above.

Your thoughts?