hi.....I have answered these posts a lot so I will try to help, N2 can always add to this.....your main concern is termperature when you go the subst. route. To maintain temp I would suggest getting a small therm from your drugstore....you can use a small travel shampoo bottle to put the temp strip on to test........if you keep the sample close to you it should remain in the correct temp region........remember too hot is ok in the test site since you can always blow on the sample to lower the temp. but if the temp is too low it is hard to raise it up.......with that said, if you still decide to use a condom, you should keep your legs crossed to try and keep the sample as warm as possible.........remember to read the temp gauge on your sample when you are at the lab, if it is too low it will be rejected.....substitution is almost foolproof, the only concern is temperature, as long as the sample your receive is clean, you should be in the "clear"

Cheers to you and good luck!