Made this up to-day. Shelf is mounted on a microphone stand, which I bought to hold mic for room correction with Dirac Live.
The board is drilled through centre and held in position by placing it on top of the mic stand with the threaded stand bolt in the hole and then a standard mic holder adapter screwed down from the top to sandwich the board.
Provides more flexibility in experimenting with height and position of Acoustic Revive RR-888 if desired.