There is only one way to do it with one Pokemon: Kecleon.
An example of doing it is in this scene:
Lucario used Toxic!
Kecleon was badly poisoned!
Kecleon used Thunderbolt!
Kecleon is hurt by poison!
Lucario used Iron Tail!
Kecleon's Color change made it the steel type!
.....Other than a battle somewhat like this, it's impossible to poison a Steel type.