Half inch RNC is pretty bendy stuff. As long as the dome has a reasonable raduis you should be fine. I userd 3/4" RNC for the bows in my boat lift cover. That has a pretty good bend in it too.
I think the 300.6 exception should ease your concerns about the 1/4"
Exception: Nonmetallic raceways, boxes, and fittings shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.
Glass is similar to tile IMHO.
