Mosaic tile install trick on uneven surface of needing build up 

I'm not a tile guy. This is not hard to see, I'm a diy guy who finds solutions to problems as they arise. Like many, youtube is my goto for quick idea when im being lazy. When I can't find a 10yr kid that knows everything on youtube I must revert to what has gotten this far in life. FIND A WAY.
Installation of tiles that will be flush with a square curtain glass shower door must be straight and level. sometimes I've run into areas that need to be built up or the wall is just uneven. My 1st 3 mosaic tiles where not square as I placed all my focus on Installation of the many pieces looking correct and uniform. After seeing that the tiles where not square i was forced to remove them. Single tiles can be straightened by prying a corner out to level..NOT A MOSAIC . All I found on line was installing on a backer. be it Schulter or hardy.
So this is a toll you can make with wants in front of you now.
It can be made with any straight edge with something added to spread the thinset at the desired elevations I hope this video helps. I'm sorry for poor quality.
Cheers Joe