Still dirty as of this morning (not even a hint of a faint line), so I guess it's time to start making a decision about what route to go. I'm thinking substitution is the less risky option. I can easily get clean human urine - and probably get it the morning of the test.

I'm a little worried about the fact that I'll have to get a physical at the same time, and I don't know how "intrusive" that will be. What do you all think about simply a flat plastic bottle and a warmer in the front pants pocket?

Thanks for the responses so far!