hey mate!
good to see a fellow pole on the forums!!
i dont know how u could go about what u want to do, but i know for certain that plain ol air tanks can be added on to compressor, but thats if they fit....
the prob that i think ur gonna have is that the fire ext. will only have one inlet/outlet, while im guessing that comp tanks have a inlt + outlet for the air. but i may be wrong, this is just a guess!!
why dont u get a air tank, and then u could fill that up with the compressor, when its full, switch off the compressor and just use the tank? thats basically what i do with my comprsser with tank. let it run till its full, then switch it off, when its low turn it on again. if i dont do this it will switch on /off every few seconds...bloddy annoying!!