Never working with exactly what you are describing. But I have worked with many other things. Here is my thought, Back cut your Mitre with a hand saw not threw the front of the trim. So when the piece is bent for the corner you would bend it and not have an exposed cut end on the outside of the corner. try it with a scrap piece and see if you can get this to work.
I'm using glass tiles around the tub as a splash guard, no shower with this tub. When I reach the height I want it to be what are the options for finishing the exposed edges of the tiles.
I've seen different width and lengths of liner accent tiles, can these be used to finish the edges? I want something thin and not the standard 2-3 inch bullnose tile. The field tiles in the shower are linen look porcelain.