Yes, I emailed strings by mail, and they discouraged the idea of putting Kling-on or anything like it between the clamp and the guitar.
However I've been using a Murata now for several days on my French polished spruce top guitar, and have no scuffs to show. I'm really liking this support! I get a slightly higher angle that's more solid than just using a foot rest. The first position portion of the neck is slightly further away from my left shoulder, and the upper positions are closer. I'm quickly adjusting and like this. Also the Murata allows some forward and backward motion of the guitar that feels natural. I went back to my foot stool and already it felt strange.
Paul Weaver spruce 2014