One reason you dot and dab is so it can squish out and expand as you push the wallboard into place. If you did it like tile, made it really flat first then added grooves, you could get away with it, but it'd be a lot of work.

Unless you have tons of free time, I'd sell the 370 eur of stuff for whatever you get and buy the carpet glue. It won't be worth the aggravation to make do.