Once, a very long time ago, I had a defective shirt on press. It had an elaborate revolver program that involved a clear gel base, a white base, all the colors and then a top gel white over everything...it was a little heavier than your average print but nothing crazy. Since it was a defect I decided "screw it, let's leave it on and see what happens."...no thick stencils at all in this setup.
Well, after an 8 hours shift it looked really freakin' cool. It was probably about 2000 microns...but this thing had gone around hundreds of times on a revolver program with essentially 3 base plates (all on 110s) and it only resulted in a buildup of roughly 2000 microns.
Phat films are a bit on the pricey side and also a tremendous pain the the butt. We switched over to high solids content emulsion for those jobs. With a buildup board we can get anywhere from 500 to 1000 microns easily. 200-500 you can do just with an exaggerated version of the glisten method.
...and depending on how high you're looking to stack you might need additional screens with a thicker stencil, or the same stencil thickness and more off contact (for just that screen)...or both.
I've only played with this stuff before at these crazy thicknesses. But without Phat Films or a heavy buildup of high solids emulsion you won't be able to do this in a reasonable amount of time.
Unless anyone else has any other tricks I'm not aware of. In that case I'm all ears.