Err, QM, you do understand that Carbon Monoxide when properly mixed with air, is an explosive as well? Chem Sniffers would register that too.
I have a very hard time believing a simple plastic bag would work, simply for the fact that if simple plastic bags could defeat dogs who could sniff out explosives there would be no such dogs. Either that, or I've suddenly become public enemy number one to Homeland Security.
If someone knows the permeation of a common zip up plastic bag, it'd be helpful on that end. My Google-fu is weak.
On hermetically sealing, the best seals utilize metals and thus would register on MADS. So we'll have to use a laminate which reduces the longevity of the seal. It would last to go through a Chem Sniffer, but it would eventually permate through enough to be detected if it were stored in one place for an extended period of time (couple months, maybe a year if it's particularly good).
Also, I'm not sure of the tempatures required for the laminate. I'm also not exactly sure of the stability of "the powerful propellant charge" within Hi-C bullets. This may be a sticking point, I don't know.
I agree with Kage that a hermetically sealled, fully ceramic/polyresin clip filled with Hi-C bullets might work until used (thus breaking the hermetic seal). Anything less and either Chem Sniffers or MADS will pick it up.
Solution? Dikote a carbon knife and give it to the Adept