This is much like repairing your bicycle's inner tube:

Clean the area of dust.  Cut a patch from bellows cloth or soft
leather.  Apply rubber cement to the patch and to the area to be
repaired, going a little beyond the size of patch.  After the
cement sets up (about 10-15 minutes), carefully position and apply.
It grabs immediately!  Rub down the patch.  Gently.  Dust liberally
with baby powder.

This is easy and it's permanent.  It does not take the place of a
bellows recovering, but its close.

Robert Linnstaedt