They shouldn't feel your pelvis area, but they will do the usuals. Blood pressure, reflexes, vision, and maybe hearing. I would start the heat pad at least 30 minutes before you walk out the door. Then just before you leave, nuke the QF for 10 seconds and apply the heat pad. Put it in your pocket and after you do your physical you will re clothe and crouch it for the UA. Just make sure your temperature range is between 90-100 degrees. I would try to get it between 96-98 to avoid suspicion. If your sample is not warm enough you can briskly rub your finger on your jeans and lightly touch it to the temperature strip.

Practicing with water will help you to get a feel for how to store your sample and maintain temperature. Definitely... Practice, practice, practice.