Drill them out a dowel and epoxi
How SMALL is your (yore) small ?
If you have a dowel cutter, the same type of wood as your stringers(most likely fir) if not any hard wood dowel is fine.
Ok. So drill the hole out, pop a dowel in, epoxy and done?
Pretty much.
If you want to be completely anal, get some resin. Coat the inside of the hole and the dowel before shoving it in.
Just pack it in with Marglass. Its not structural. If you use a dowel let it equalize the moisture. Ive done it and they swell and pop the surface.