Here's the good news - you don't have to use dry ice. Here's another alternative for making a CO2 chamber. Again - this states that CO2 is recognized as a HUMANE method of pre-killing your prey.
I personally will never support bashing or stunning of prey. I don't care if someone doesn't have feelings for the prey - it's cruel and not necessary when f/t is available to purchase and a CO2 chamber is so easy to make.
I feed live, and I've never stunned a prey item.
http://www.thereddragonsden.com/co2.htm