Current Interpretation 2 of the class rules says yes. It's funny, though, that it uses the same picture as one of the cases of "Illegal Equipment"!
It's supposed to prevent wear of the deck, but it's really the traveller block that benefits more. You'd probably want a sticky material, too, to keep the block out there... this could actually be a loophole for some interesting pieces of equipment. We'll see how it turns out.