Smoke em,
Get a 2 liter bottle, use a knife to put a 1/8 inch hole in the lid. Pour half full of WARM water, not hot. comfortable to the touch. Put in 1.5 cups of sugar, and 1 packet dry active yeast (availible at any grocery store in the baking section. $1.00 a pack). Let the sugar dissolve before adding yeast. Place cap on bottle, shake it (cover the hole with finger!) and set it ABOVE your plants. CO2 is heavier than air, and it will settle on top of your plants. Lasts about a week. Repeat.
Make sure you have an airtight to semi-airtight room, or it's not worth the effort.
Peace
TeNn
Oh yeah, you can do this with like 3, 2 liter bottles. You'll notice a difference, I do.