Come to think of it, I have had some success repairing holes in wool sweaters. One of 'em you can't even tell, and I'm no expert with the needle and yarn. I got my advice from browsing YouTube videos. 

Anyway, I bet I could use the same technique on merino wool, just use lighter yarn. Basically you just work from the strong, undamaged part of the knit and criss-cross the hole. Some magnification would probably be handy for something like a light base-layer knit. Worth a try.

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.