I always found the backpressure of nitrous balloons to make using them really unpleasant.
What I did was take a 2.5gal Hefty One-Zip plastic bag, and a nitrous filter attachment (ostensibly for filtering nitrous used for cream whipping), and a short length of tubing that fits the bottom of the filter attachment.
Affix tubing to outlet of the cracker (aka filter attachment - the one I have perfectly fits a 7/16th inch diameter tube).
Cut hole in bottom of bag, put tube in, seal with duck/gorilla tape.
Seal bag, empty 2 crackers into it, and load a third. Lay down, open bag 1 inch (it's only ever open 1 inch, so you can't suffocate yourself with it) and take a deep breath, and then reseal bag, and pop the third cartrige (since there's now room in the bag for it) while you're still capable of doing so. Enjoy three cartridges of nitrous without having to fumble with a balloon or cracker. It looks ghetto, but it's much more effective and comfortable than any other mechanism of using nitrous that I've encountered.