Mark, I don't normally pin WA handles, but if I were to, I'd do it like I do any other hidden tang handle and mount the knife in a fixture that holds the blade elevated at the ricasso. This way I have room to slide the handle on the tang while the blade is mounted on the drill press. I have already drilled a hole in the tang a few thousands over prior to HT. With a bit sized for the pin I want to use, I line up the fixture on the drill table so that I can lower the bit through the center of the hole in the tang. I secure the fixture in this position and slide the handle onto the tang butting it securely up to the shoulders. Then I can drill down through both the tang and handle. You have to be careful of tear out on the bottom of the handle. I normally tape the bottom, but on a finished handle I'd want a block of wood under it as I drilled through. Of course with a WA handle with a taper, you would have to be sure your handle fit up had no slop and fit tight to where you wanted it prior to drilling the handle.
Hope this helps!
