I don't think the sawdust idea will disappear upon finishing. It will probably come out as a dark stripe. Are you certain this is going to show? There ain't much wood on these guns and lots of times I have thought a boo boo might show up, only to discover it will disappear when my final shaping is done.
For the ones that you can't scrape or sand out, a real piece of wood is usually your best bet. Also, Taylor turned me on to using a magic marker to blend in boo boo's. (I know, the horror!) Between brown, black, and red, rubbed with some lacquer thinner, you can make an area look pretty good. Practice on some scrap first because that stuff soaks in and is very permanent!