Gee folks, reminds me of the story just before Y2K when a guy packed beans and rice in PVC tubes and felt the need to put dry ice in each tube. he then placed them in his garage until new years. His timing was off, but the fireworks were fabulous.
Seriously though, if you have a dialy available supply of dry Ice, use heavy duty ballons T-eed in to your air line as accumulators, small amount of pressure large volume. figure out the regulation for release into the tank, and then you can let the dry ice melt, and fill the balloons then as the co2 is used the balloons deflate. The big question is where to hide it. The worst thing that could happen if you make a mistake would be a loud bang, and a loss of some co2. BTW remember if you lose large volumes of CO2 in an enclosed space it would be best not to go in a try to breathe right away. Co2 is obviously harmeless to breathe, but it disperses O2 and can suffocate you harmless or not.
dave