I'm about to build a GP Extra kit. It uses lite plywood circular discs to refine the location of the dowels. You have a thick former with oversized holes - bigger than the dowels. This allows movement of the wing to make sure that it's aligned with the fuse. Once aligned secure the wing to the fuse. Take the discs with holes in the center - holes being exactly the outside diameter of the dowels. Slip the discs over the dowels and press against the back side of the former. Tack the outer edges of the discs with thin CA - just enough to hold the disc in place so it will stay in place when you remove the wing. After the wing is removed thoroughly glue the discs to the former with CA.

I used a similar technique when I converted my SIG LT-40 from rubber bands to nylon bolts. Worked well.