What I did was add a few tablespoons of sulfur to the coals in my smoker and
then shake it up.
Smoke from this was blown into the hive rather densely and then the openings
were taped shut.
Next day there were a few bees at the entrance that had been outside and a few
bees that were not quite dead on the inside amidst about 10 pounds of the
dead.
Sulfur is available at garden supplies as a fungicide.
 
I should imagine one could kill a hive with a plastic garbage bag- their own
respiration would do them in.
 
Grisly work for a beekeeper no matter how it is accomplished.
 
Tom