Fellow (almost) CDL holder. I face randoms daily at work, as well as the annual and heaven forbid, post accident test. The answer is to substitute. I'll post links, but DOT are not observed except with cause. Substituting for a DOT test is easier than taking candy from a baby. If you havn't yet, read the SUBSTITION: tips, tricks and guidelines I posted on the main board. Then if you don't have access to free clean urine, order it on the web. Remember for free pee that age or sex of the 'doner' is irrelivant. All that matters is that is is drug free. Urine will store at room/body temp for up to 8 hours and frozen for up to 1 year.
Here is a link to the DOT regs that will rule your life as a CDL holder. Read them!!! http://www.dot.gov/ost/dapc/main/CFRintro.htm (use either the PDF or WORD version)
Here is the specific reg on observed test. http://www.fmcsa.dot.gov/rulesregs/fmcsr/regs/40.67.htm
Here are links to urine on the web. Either synthetic or human will pas the test, but personally speaking, because of conveniance, I never 'clock in' without a bottle of Quick Fix in my pocket.
Quick Fix: urineluck.com (while your on this site, check out their message board)
Dr. Johns: urinator.com (you only need the concentrate urine, not the urinator)
Cheap kit: 420-heaven.com
Human: pretestedurine.com
Human freeze dried: pass-any-urine-drug-test.com

Hope that helps. N2