Ok pretty simple science here. In a bottle/container with a lid place some dry ice. Seal it and attach a tube. Cut small holes/nicks in the tube for the co2's release. Drape around the plant and tada!

Remember, Dry ice is solid c02 and it sublimes directly into a gas and its xtremely cheap.

Only question is will the gas be to cold and harm the plant?

Give me some suggestions and ill try it out on some basil.