Subject

After rereading and hopefully understanding the problem, short of
opening a seam thru that 1-1/2" plywood, as others have suggested, you
can't get there from here.

Unless.....................

You approach this problem like drilling a well, only horizontally
which will require significant cost to built all the componet parts.

Opening up a seam will probably less costly.

Back to basics, why is drilling necessary?

What is the purpose?

Lew