When you say wet sand for the binding, how are you keeping your sandpaper over just the binding? Or have I missed the point?

As for a scraping jig... last night while I was wondering if it would work or be worth doing, I made this thing out of a chop stick, and I think it's going to do exactly the the job. I ran it round the edges of some offcuts and the blade didn't slip or rotate or anything, so I might give it a try when I get the chance and see what happens.