Pour about an inch of sawdust into the old cup.
Squeeze a dollop of ordinary wood glue into the cup, or use a specialized resin.
Mix the sawdust and the wood glue until it has a uniform color. Add more glue if the mixture does not bind. Add more sawdust if you have too much glue.
Scoop out some of the reconstituted wood mixture with a putty knife or similar tool.
Apply it to a cleaned-out hole in wood, such as on your window frame. Fill the hole until it is approximately flush with the surrounding area. Sand it level, if necessary, when dry.