Well, here's the story. I tried filling the hole with a sawdust mix and could not get the color just right--that white wood shows just everything. Then I cut the piece down the middle to try and disguise the hole, but that didn't work out right either. So I scrollsawed the piece out, backboard and all. I glued a piece of backboard to a new piece of aspen and cut out a new piece. It actually fit better than the old piece, sad to say

Then I put a big piece of backboard over the entire back so daylight wouldnt show through the cracks where the backboard gapped a bit.