Luckily, I had a big balsa block from when I had to rebuild one of the wingtips on this very wing last winter. Now, even though balsa is technically hardwood (look it up!), it's not especially hard or crush-resistant. However, even the little cautionary voice in my head agrees that this is not a problem - the sleeve will prevent the balsa from being crushed, there is plenty of surface for glue adhesion between sleeve and balsa block, and the balsa block will be glued to the wing on four surfaces.

Here's the shaped block.




Glue in, skin on.




I decided that the other wing would have to be done too. Note the makeshift clamp to hold the balsa block against the internal leading edge.



Next step will be to reattach the wing and drill the new holes.