When the tablets disolve, the CO2 remains in the diffuser, where it slowly disolves into the water over a period of a few hours. I don't know how good it is, but you will see the water level in the diffuser slowly rise as the CO2 gets used up. The only way I can think of using it, is as Themuleous says, make up a DIY kit using a bottle. Then you could feed the CO2 to the diffuser via the hose. You could either feed it down the shoot for the tablet (would look a bit messy). Or you could drill a hole at the bottom of the unit (under the gas chamber) and then feed the hose into there and seal it with aquarium safe silicon. To be honest, I would buy a dedicated diffuser which has a hose fitting on it already if I was going for the DIY setup.