Another option would be a completely controlled set of CO2 inlet as used in many planted aquariums.
I know my brother has a system like that, 'feeding' the plants the dissolved CO2 as it were. This is just a small gastank with CO2 (available @ the petstore) with a controlled outlet.
Should you work with either the bio-way or the chemical way, it would be wise to bubble the produced CO2 through some cold water, and next through a piece of cotton to prevent other things than CO2 comming through, and maintain a sterile environment.
It would look a little like this;
CO2 produced in A (either chemically of biologically through fermentation) is washed with cold water in B and filtered (optionally dried with e.g. CaCl2) in C.
From here on it will be passed through to the set-up.
The CO2 can be bubbled through a liquid medium, or just let free in the air part of the set-up, I don't know what the intention is here?
Kind regards,
Remko.