Hmm, I think I'm gonna have to pick up a few old extinguishers, that sound's like a hell of a good idea, I usually sit it in front of the space heater until it's nearly too hot to handle so it's a lot thinner and easier to pump in.Another use could be to fill them with EP90 gear oil and pressurise them, giving a handy device for getting the thick stuff into gearboxes etc on vehicles.
I literally just thought of this, and will do so with one I have somewhere.