It depends. If they are testing the T/E ratio then you should be fine. If they test for metabolites then there is a possibitlity it would show up.
To start flushing the system you need to keep your metabolism up. Working out, eating good at least 6 times a day. And, I would say that DNP would help flush the system also, but this is only a theory.
The week of the test do not do any exercise - this will put the metabolites in your blood stream which will be excreted by the urine. Just be lazy and eat. The day of the test drink lots and lots of water to dilute your urine. Take vitamin b to color your urine(this is not extremely important because clear urine is not too uncommon). Also, they will test your urine for creatine to make sure the sample has not been diluted. To avoid this, eat lots of red meat the day of and at least 3 days prior to the test.
Good luck
Nauitca