I've done this before- I picked up the loop with a spare yarn, did a small knot to prevent the loop from unravelling, and wove the ends of the spare yarn into to the rest of the knitwork. This was on a dog sweater, and the pulling up of the dropped stitch simply looked like a natural decrease-- and after many times putting it on and taking it off of the dog, washing it, etc-- the stitch has not come loose.