if you can get the clamps on firm with perhaps rubber /friction matt /other grippy material between board and cill this will give maximum resistance against slip
then move the pivot point from the nose off the cill as far down as possible by padding out the gap down the wall between clamp handle and wall with something hard then this will act like its screwed to the wall
then move the pivot point from the nose off the cill as far down as possible by padding out the gap down the wall between clamp handle and wall with something hard then this will act like its screwed to the wall
