Smell it you can DEF determine the smell difference, also most at home tests come with a box you can mail to the lab you can do that too..
I'd say taste but thats just DISGUSTING
Don't tell him your doing it ahead of time. Wait until he just gets home or just gets out of the shower or something. He can't have the Apple juice with him at all times. If he doesn't have to pee make him drink water and don't let him out of your sight.
Stick one of those thermometers made for foreheads on it. Although one could hear the apple juice, it's doubtful they could get it close to body temp. It will be under or over quite a bit I'm sure.
A test that measures creatine, a protein synthesized in the body, is how most people fail from foreign urine or alternative liquids.