Most likely its not as effective as the yeast method (which would be cheaper). I wouldn't try it....I don't think the co2 levels would be enough or steady.
On a 10g, 2 2L bottle setups would be pretty effective. Don't go too long before changing the mix (a few weeks at most) and you should have a pretty steady co2 level.
I used juice bottles on my DIY CO2 setups. They have a flat bottom and are sturdier. Get some airline, a t-splitter, and check valve and put it all together, much like this:
http://www.plantedtank.net/articles/DIY-Yeast-CO2/7/.