I’m pretty sure you will not be able to smuggle pee in. On the several occasions I have taken drug pee tests (a couple times for work, but lots more because that’s just my fetish {kidding]), a lab assistant is in fairly close proximity, and they take the temperature of said pee with a thermometer on the side of the container.
If you do decide to freeze your friends urine, just don’t put a stick in it, especially if there are children in the house. There is nothing more dissapointing on a hot summers day than to end up with a peecicle.