AMS and MSO
You might try AMS (ammonium sulfate). It is supposed to make all herbicides work better. I don't know the technical term, but herbicides don't work well with really hard water and AMS cures this......ties up ions or something. supposed to be really critical for gly.
Also add a sticker like crop oil (coc) or methylated seed oil (MSO). It keeps the gly on the leaf longer and helps break down the waxy leaf cuticle for better absorption.
These are additives I've used in commercial crop spraying for corn or beans, so I'd have to do some number crunching to figure out the rates. But, around the house I've used 4 tablespoons of olive oil or veggie oil in in a 2 gallon sprayer and it really works fine as a sticker. You gotta shake the heck out of it because it doesn't disperse nicely like a proper commercial sticker, but it does the job.