[yourMadness]

You could add 80% nitrogen and 20% oxygen to dilute the CO2 to the desired level.

But that's not exactly easy or cheap. And dangerous when done wrong.

[rufus_foreman]

How exactly would I do that?

I'm OK with not easy, not cheap, dangerous, and done wrong.

[samatman]

As long as you're okay with not cheap, Alfaintek has you covered.