I personally like the toothpick idea, only I'd use thin CA. Drill 2-3 holes in each side of the hinge, push the toothpicks through, and put a couple of drops of CA on each one. Cut the ends of the toothpicks flush with the surface.

This will work fine for a trainer. If it was a faster, more maneuverable sport plane, I'd recommend replacing the hinge or cutting the rudder off and rehinging all of them.

Dr.1