By - Anti-meatbeater
Superglue would be good for something like this but you might wanna look into hobby cement for any future mistakes, it can be quite a life saver
Website that sales individual parts of the runners.
I'd give it a shot, I've made an open hand into the "spider-man web shooting" gesture by snipping off and re-glueing the fingers, so it might work.
So long as you keep in mind to handle gently, super glue should be fine. Depending on your intended pose and what it's holding, it MAY work better to glue to finger to the gun itself and hide the gap with some clever posing.