Well, right off the top of my head, do a search on the forum here for "Lucky Boxes" with are some hard wood inserts that are built into the flaps so that you can use a common horn assembly. The inserts are wide and are slotted horizontally so that as the flaps actuate the arms of the joiner don't bind andthey will move freely. They are called Lucky Boxes because they were conceived by a gentleman named Lucky Pyatt who was a noted southern California stunt flyer.

  Making the flaps more barrow would be in order but mare make the wings look funny?  An option would be to build out the trailing edge, even if it's kept flat. Limiting the throw would help some also. The SIG Fazer was flown quite a bit as a C/L stunt model and I think Mike Pratt designed it as such and the instruction and plans that came with the kit showed how to convert to C/L. The airplane may fly OK but depending on airfoil and such, I would not expect too much out of it.
  Type at you later,
    Dan McEntee