Just cut a piece of 1x2" board about 12" long. Cut an "L" shape on the end that will ride over the thicker tile, which you put up first. Scoop in some thinset into the "band" area with a margin trowel and "adjust" or screed it with the board.

Let it dry. NOW, you have a slightly raised area upon which to tile the glass and it will be the same height as the field tile.

what my tile setter did was to use some of whatever the backerboard was 1/2 the thickness of the tile and set the border tile on the backer before he put it on the wall. then he installed the border already completed and it came to the same thickness of the wall tile

Good Luck
Rachel

Your tile installer should have no problem making up for the difference of thicknesses if he knows what he's doing. This is tile 101.

We used a similar thin tile against a thicker marble tile. Our tile guy built up the wall and we love how it turned out.