The easiest and cheapest way to use CO2 as a fire ssuppressor would be a small (< 5 pound) extinguisher) wall mount unit about waist high, five to ten feet away near the power supply to the machine. If a fire starts that the airjet fails to extinguish you cut power to the laser AND airjet, a three to five second burst from the extinguisher (more if needed), start a high-flow exhaust fan and leave the room. Pros: Cheap (cost of extinguisher), simple and easy to use. Cons: Multiple steps/locations, relocating power supply/exhaust fan switches.
Or set up a "Panic Button" that when pressed: cuts power to laser and airjet, releases a three-five second burst from a permanently mounted, small (20 pound) CO2 tank and starts a separate high-flow exhaust fan to clear smoke/CO2 from the room. Have it near the door if you have to press it again it the first burst doesn't extinguish any flame. Have a small container of water nearby in case the wood reignites even after multiple uses of the extinguisher. Use only as a last resort as water plus electronics is NOT recommended!
Panic button Pros: one-step, easy to do under stress, you don't have to refill extinguisher after using (yes, recommended after any usage however small!) and while you're heading out the room! Cons: Costs, electrical and mechanical hookups. However, it would be a one time fixed cost that has the added advantage of possibly reducing your insurance rate. The rate reducement might even pay off the initial costs within a couple of years.