All my hops are zipped up in airtight bags and stored in the freezer.
I chuck them straight into the boil from the freezer - they are going to go into a solution that is at least 80C hotter than the room they are boiled in so the extra few degrees being frozen will make stuff all difference - so far, no probs.
I must admit though, that using CO2 will probably help in keeping the hop pellets and plugs fresher than sealing in O2...A wise head once told me that if you can still smell the frozen hops, through the seal, then you haven't properly sealed the container. If I want to get real pedantic about storing the hops in a jar, you can wax seal the lid just like the missus does with her jams.
Cheers,
TL