Here are some pictures that will help. Before I drill the hole I perforate the wood where the joiner wire will be installed as the other guys have stated and saturate the area with thin Ca then I take two pieces of 1/64" ply rough sand and laminate the pieces to the top and bottom of both elevator half's using 30 minute epoxy let dry (set up)
Then drill your hole. As ChuckW said start with a smaller guide whole first, If you are worried about what you have already done, it is easily repaired, just sand a 1/4 square piece for balsa down to the same size or a bit larger than the whole you have already made than with a little white glue on the balsa dowel you just made push it in and let it dry. Then sand off and re drill the whole. I would laminate the light ply as in the pics first. before re drilling I have used this method on Full kit built and arf planes. I hope this will help.
jerrysu29 Call Sign Wild Man