Possible to use trim with routed out channel to hide 12/2 or 12/3 wire instead of using Wiremold?
No, you can't do it unless there's a &quot;nail plate&quot; to protect it from physical damage (nails).
You could mill it out to 15/16&quot; and lay in EMT metal conduit.  It has the thinnest wall of any conduit and will provide the needed physical protection.  Use that either simply as a damage shield in the vulnerable area, or if able, as a full-on wiring method for the entire route.