According to one site:

Chlorinated bleach will test negative, and it's the best household additive. In an emergency, Jeff Nightbyrd recommends adding unscented bleach crystals to a diluted sample. It's recommended to grind the powdered bleach to a finer grain. 1/4 teaspoon is recommended for a 60cc sample. For liquid bleach, add six to ten drops. Bleach will throw the pH outside the normal body range; so it may be apparent that the sample was tampered with. Some bleaches foam or leave residue, so experiment with different brands before selecting which to use.

What that means: Get a hold of some of the test strips and find out with your own trials wether it will work or not, and the best way to do it.