The short answer is that no, you can't. There's a long chemistry explanation as to why, and it has to do with how different gasses maintain pressure. The gist of it is, if the propellant remains a liquid in the magazine, then it will maintain pressure until all of the liquid changes to gas. That's how Propane, Green Gas, and HFC 134a work. That's now how CO2 works, however. Those CO2 cartridges contain gas rather than liquid, and every time you shoot some out of it, the pressure in the cartridge drops. That's not a big deal because the pressure is very high, which is where the regulator comes in. If the pressure in the cartridge is 300 PSI (this is hypothetical, I don't know what it actually is), and the regulator allows 120 PSI through, then as long as the pressure in the cartridge stays above 120 PSI, you get full power shots. The pressure in the cartridge will drop with every shot, but stay above the regulator's allowance for a few mags.
What this product does is, it regulates the CO2 before putting it into the reservoir of a mine/grenade, or hypothetically a pistol mag. It allows (hypothetically, but probably close to) 120 PSI of CO2 into the device. For a mine or grenade, that works great because you're only firing it once before recharging it, so you're blasting all of the gas out of the reservoir. With a pistol, however, you want to have multiple shots. The problem is, every time you shoot the gun, the pressure in the mag drops. Your first shot might be at 120 PSI, but your second might only be at 80, and your third will just dump the rest of the gas. There's nothing to maintain pressure in the magazine. It would act like a propane powered GBB on it's last couple of shots. One near full power, one half cycle, and that's it.
Unless you're dead set on CO2 I would highly recommend using propane instead. CO2 will put much much more stress on your internals, and lets just say, WE is known to be "not be so good." Propane is also a lot cheaper than CO2 cartridges.
Ok. It's just that I've gone through two Propane adapters, both of which were the good Madbull ones. The first time was my own doing, I dropped it and naturally the tip broke. The second time was when my dirtbag "friend" shot it, said "oops" and didn't pay me the $20 for it. I really wouldn't have cared whatsoever if he'd broken it and gotten me a new one, but he broke it right in front of me, (he shot it with his airsoft gun to see what it would do, the brilliant bugger.) then said it wasn't his fault and wouldn't pay for it. but besides my personal issues, I guess I'll just include a propane adapter and some silicon oil tomy next purchase of airsoft equipment.