C02 into undergravel filter?

I'm thinking of adding DIY yeast CO2 to a 29 gallon tank.  The tank has an
undergravel filter with a power head.  Has anybody tried sticking the CO2 hose
into an undergravel filter in order to mix the CO2 into the tank water?  The
tank has java fern and mexican oak leaf attached to drift wood; so no comments
about undergravels being bad for plants :)  I guess my main concern is that 
that white stuff that builds up at the end of the CO2 hose from yeast systems
would be a problem in the undergravel.