Just drop the c02 cartridges down your seat tube, stuff a long piece of rag down to stop them rattling. Job done.
Mostly when you check-in you should ALWAYS be asked if you have any of the following items which include pressurized and gas canisters, lying as result is a criminal(not civil) offense.
The deal is the canisters could burst under pressure. Most all large modern planes has pressurized luggage holds, so it a non-issue. Things do and can go wrong though. Many old turbo prop planes, and some older jets do not have pressurised cargo holds. Your bike mike get put on one of those as a connecting flight. However, none of these planes fly at high enough altitude to exert enough pressure on the canister to cause it to explode, unless it was faulty from manufacture.
Even if the cannister did burst during flight, it doesn't have enough pressure to break through any material that planes are made from, unless it went off right next to a fault in the planes construction.
So, net net, theres a very small chance of it causing damage. However, thats the reason why planes generally don't crash, the airlines don't take calculated gambles. It's no consolation to the relatives of a couple of hundred people should it set off some form of chain reaction that caused the plane to crash.
Putting the cartridges down the seat tube will ensure that if it does explode mid-flight, it will not cause any further damage. A C02 cartridge doesn't contain enough pressure to blow through a steel, aluminum or carbon frame and then cause secondary damage.... unless....
Hey, and if you quote me, I'll deny it and claim my computer was hacked.