If they wont stand up on their own that probably means they are pretty stretched, try moving them closer to the lights.
Get them as close as you can without burning them.
With CFL's you can usually get within 4" and still be ok.
A lot of bigtime growers use a slow relesae CO2 system to aide their plant growth and it does work.
But the paintball canister (unless its a big one) will need to be refilled every few days i would think, and that is just a pain in the butt.
Another way to generate CO2 is to build a small "Generator"
Basically it consists of a few items
1gallon container with a fitted lid.
5 cups sugar
couple tablespoons of ACTIVE yeast.
Throw all the ingredients togehehr in the 1gallon container, throw in half a gallon of water.
Shake/mix it up well
Cut/melt a hole in the lid of the container about the same width as a pencil.
In a few hours you will start to see the concoction start to "fizz", this is the yeast turning the sugar into CO2.
Give the container a shake every once in a while to release more co2.
If it stops fizzing, the mixture needs to be replaced.
Usually good for 2-3 weeks.