try caoting it out in some two ton, slow setting epoxy. coat all of the wood evenly and make shure the gap is full. you might try laying a little bit of thin balsa over it as quasi sheeting(mainly on the bottom to keep the epoxy in and smooth).

thats what i did on my horizontal stab, and it has held up well. especialy considering my instructor took it out and intentionaly tried to break it to mak shure it was gonna hold.