Repairing a cracked, damaged or worn wheel
The wheels wear out and are no longer usable after 1-2mm are worn off the sides.
Light wear and cracks
A quick fix might be to spray paint a worn wheel with a polyurethane coating. I have no idea if this would work: http://www.utilitysafeguard.com/K07120-Clear-Polyurethane-Coatings-Matte
I could be wrong, but paint is general 0.1 to 0.2 mm thick. This would require many coats to achieve 1mm.
Heavy wear and notches
It is possile to use M-1 sealant from bestmaterials.com to fill gaps, cracks, and flat spots.