You can let it cool to room temp as much as you need to practice. No need to put it in a refridgerator.

You picked the right one, if I may say so myself. Its the easiest and most surefire way to pass your piss test, so no worries. Once you get it in, do a few mock runs of the heating, keeping the temp right, and procedure to remove it from your "hiding" place so you can pour it. I also recommend taking the cap ENTIRELY off when you go to pour it, so you get no suction noises, thats a deadfire give away.

Practice makes perfect, and remember to have a proper demeanor when entering the testing facility. Dont draw attention to your hiding spot, and act normal. Act like you are there just to take and pass a piss test, and its the norm for you. If you act like you know you are going to pass(not overly so, just dont be nervous), and act normal, you are all set.