Just a heads-up I seen something for sale that looked pretty good. It's a small bucket that has fungi or something inside there that releases CO2 at a good rate for a few months.... it was a grow product and cost £100, you can find it on a few websites but im not sure of the exact name.

I've also heard of using carbonated water is feeding but I havn't looked into it. Would be interesting to hear more about the club soda..