I'm not familiar with flash board installs, but could you drill a shallow blind hole (or two) in the boards that would allow a piece of all-thread to be screwed into it, install it, and then unscrew the all-thread hence removing your installation tool? Just bouncing the idea off of you. If you needed it to be long lasting for future removal, maybe a stainless steel nut like this from McMasterCarr...

https://www.mcmaster.com/#98007a033/=19h9khq

could be recessed and screwed to the boards using the holes in the mount plate.


Fish on!,
Noel