hanging my tomorrows on the bones of yesterday

You're right. I used a little hyperbole there. What I meant was "they both kill easily and painlessly," not "they do the same thing." You'd have to follow similar procedures with N2O as well, they'd just be based upon the fact that usage of N2O is regulated instead of the fact that CO is dangerous in small amounts.

Your "handlers" would just have to wear oxygen respirators like firefighters have.

In the end, I think I'd be able to drum up more support for a CO death sentence than a N2O death sentence. Most people who support the death penalty would probably argue that N2O was too much fun.