Straps x Surfboard on top of GFC / No Beef Bar?

I am looking to transport my surfboard on top of my GFC without the beef bar (not enough clearance in my garage.)

I am looking for the most robust way to mount 2x flex straps from side to side, mounting the board (bag) directly to GFC roof on a piece of foam.

What setups have you seen or can recommend to attach the straps to the upper side GFC rails?

Thanks for any pointers!