The coffee creamer idea works great, but you need a way to keep the particles directionalized. If the "cloud" starts to move with the airflow in the room, you could lose control of it. BTW, the mouse uses coffeemate (Cremora) for their dragon effect at WDW, Basically it is an paint airbrust with the paint replaced with the coffeemate.
Liquid Flame projectors would be a bit more of an issue if you want the whole thing to burn to the ground. Prism flame units are awesome if you want to "color mix" your flames with Isogel, but AFAIK they dont have remote nossels.
OK, with an airbrush-style setup how hard is it to direct the flow of the coffeemate? I'd assume that with controlled air supply I can control how much creamer is dispensed by this sort of setup, but this is an outdoor production (no way would I even consider a full burn indoors!) in an area that's fairly well sheltered from wind. Assuming an airbrush setup, (and of course I'm testing this today so long as it isn't raining) can I expect a more directed jet of coffeemate?