On wood motor mounts, what I do, is dribble in a little baking soda into the hole and then a drop or two of super glue, then some more baking soda followed with some more super glue. Then let it sit for a hour or two to ensure it is all cured real good. The baking soda chemically reacts with the super glue and forms a hard plastic like substance. Then you can redrill the holes as needed. You can even drill and tap the plastic like stuff that is formed too. I have used this to fix numerous engine mounts and holes over the years.
Baking soda and super glue makes for a good gap filler too. But it is harder than balsa wood though, so you have to be extra careful sanding it.