first thing to check is if ur getting a urine test or hiar test... seeing that its a federal job.. they might do a hair test. or observed urine test (from wat ive read.. i think federal job tests are observed?)

im 22 and ~245lbs. it took me 2 weeks of exercising (5days a week) and another week (no heavy exercising, just walking) to start passing home drug tests.

so like u said subbing might be ur best option. im hearing diff success stories on QF, so im not going to risk it, and use a friends urine. also if u can find out wat lab will be doing the test, u can check their protocols and stuff.

i still havnt taken my test... theres some problems with my application so the test is getting delayed... its going to be either end of this week or beginning of next week.
im trying to get it a little delayed to clean up some more.