Love the new names.
From what I've found, it does seem like this could work.
So, what Stormlight healing does is it realigns the Radiant's body with their Spiritual aspect. WoB:
RoW and OB spoilers:
I also happened upon this WoB. Apparently, if you were to change someone's mental image of themselves enough, they could become a Listener in the right circumstances:
There are other instances of things like this, but I think that if it's possible for someone to change species through their self-image, it should definitely be possible for them to become more muscular if their self-perception changes.
Anyway, that's the conclusion I came to. Feel free to do your own research.