Well, this is very a thing Papyrus didn't want to find, when he came over to see what all the noise was about.

So far he's found one reliable way of taking his mind-controlled brother without killing him, and it's regretably an inheritance from the time that he did... But while people spend their time fighting more directly, Papyrus focuses his limited power into trying to form a bone of dust. One of near catatonic sleep, hopefully something deep enough that the Mother of Invention can't force him to act through.

He keeps to the back, tries to make it look like he's summoning a barrage of regular bones, and keeps watch for a good chance to get in close and thrust the dust into Sans' face.