So you warm it up beforehand, rubber band some Hot Hands to the bottle, either tape it to your leg or wear baggy pants and be slick about emptying your pockets (nobody is going to pat you down, though they may ask you to turn out your pockets, so taping it to your leg is the way to go), and piss a little in the toilet first if you're that paranoid. No workplace is ordering observed tests, that's the parole system.

You aren't wrong the only 100% way is to take a break more than a month before. But some people have a medical need, and for those people, fake pee is 100% the way to go. Dilution, cleanses, all of that stuff is way more unreliable than sneaking a warmed up bottle of fake pee in.