Why would you bother? There is no advantage to using anything but air, unless you get moister in your air, which could cause problems with you gun. Nitrogen does have advantages when used in gas ram guns, but no other advantage that I can think of, although I have heard some have tried that in their pcp’s. The oxygen, of course, would surely increase the likely hood of you reaching your final destination much sooner; not to mention those that might be standing next to you........
Jim