How many layers of sinew? If not too thick, and you have kept it nice and dry, I think you could skin it. For the last bow I skinned over sinew, I used TB 3. I did just as Pat suggested. Sized it then put on another layer then applied the skins. I think it worked out really nicely. I've used the TB hideglue on a unbacked bow and it worked really well, but have heard horror stories about the TB liquid hideglue and sinew. So I would use real hide glue or TB3 and stay away from the liquid hide glue.