If it was me, I'd change employers, find one with a less stringent testing policy.

Another option would be to pass this next test (as you are clean), then play the odds with timing and dilution methods. Also find out what will happen if you test positive. Most companies won't fire you if you fail, but require "treatment" and more testing.

You could try to meet with the CEO of your company, and ask him the same question that you ask above.