This is the result of some inspiration I got from my buddy JimLev on roadfly.com. Take a look.
This is a split nut with an integrated handle. Since only the brass nut on the nitrous line failed I really only needed to replace the brass nut. So I modeled this little gadget and cut it out. Now I don't need a wrench every time I want to fill my bottle.
I used superglue to hold it together, but that didn't last. A quick visit to the machine shop made things more stable.