Friendly Plastic pellets congeal in hot water to become a malleable mass. Form a small lump (you can use a small flat wooden block as a base if needed), and clamp it lightly against the intended area, such as an interior soundboard brace. In a few minutes it hardens into a tough, perfectly seated reusable plastic caul that can be clamped at full pressure.
The braces won't be damaged, and you won't have to spend your time making custom wooden cauls in complicated shapes. You can make perfectly seated cauls for clamping bridges, braces, fingerboards or curved surfaces.
Plus, Friendly Plastic can be reshaped again and again just drop it in hot water.