Honestly wtf does the glue matter when people are going through plastic like it's nothing? Bringing up the glue is such a weird nitpick.
Do nothing: 10 pounds of filament poop has go to the landfill.
Do this thing: 10 pounds of filament poop still exists, + 8 pounds of glue sticks (which is basically a thermoplastic) used, to create something that's eventually going to end up in a landfill.
Are you being deliberately obtuse?
Recycling or reuse is not as useful as just not creating waste in the first place.
Why use glue at all, he should have done this using a 'stained glass' method. Build some kind of a frame for each area of color and then melt the filimant into it.
When the ratio is almost 1:1 it is a bit more than a nit.