See if a fellow restorer is interested. That will work with some puzzle of appealing scenes or famous brands or interesting cuts.
Recut the puzzle to be interesting. Cut the large clunky pieces into more interesting smaller ones if it is a nice scene and would be a pretty good puzzle.
Reuse the front. Sand off the image and paint something on it, if nothing more, select some colors and spray paint pieces randomly. That would be a rather hard puzzle that someone might enjoy.
Save the pieces for artwork. Artists frequently are looking for spare pieces for their collages. Maybe you can create interesting puzzles from fragments that could be made to interlock.
If the pieces are large, save for replacements for other puzzles.