If I remember correctly, On the Myth Busters, one guy ate 3 poppyseed bagles, and the other forced down a whole pound of poppyseed cake.
Both then tested positive for opiates using a home test kit, just a matter of how much time elapsed befort testing postitive. Obviously the amount of time it took to get a clear test took much longer for the one who ate the cake.
FAA uses a 2 stage process, where the first stage is not much different than the home test the Myth Busters used. The second stage is a mass spectometry test, when someone indicates drugs on the first stage, and is much more accurate. I would guess that poppyseed rolls could kick a positive on the first stage of an FAA drug screening (dependant upon how many rolls were eaten), but do not know how it would react to the spectometry test that is the second stage of the FAA process.
My best advice is to not eat anything that might be questionable for a few days before your medical exam. Opiates dissipate from the system fairly quickly, and would then not be an issue.