Question: I plan to add some lighting in positions on the ceiling that doesn't have nearby wire available.

The there is no free space between the ceiling/roof in which to run a wire (there's the wood, then solid foam block insulation, then weather barrier, then the shingles). So, I would need to run wire (12/2 or 12/3) to that location somehow. I'm aware of Wiremold, but that wouldn't look very good with the style and material of the ceiling itself.

Is it possible, instead, to run the wire through a 0.5" channel routed out of a 1x1" piece of wood and affix that wood to the ceiling? I read through California electrical code (I'm in San Bernardino County, California), but didn't see anything specific around this (unless I missed it, or interpreted it incorrectly).

Thanks in advance.

Answer: 
Yes it's possible but it wouldn't be code compliant if it's 120v. Wires must be 1-1/2 inches from the surface so that you won't hit them by mistake with a screw or nail. If you had some sort of metal conduit you could do it. Low voltage wiring is fine.
It might require a larger trim than you were thinking but have you considered just increasing the space in trim to accommodate the wire mold? This should be doable with pretty typical crown molding. If you need to run across the ceiling you could add a coffered ceiling which can look really nice.