...or going one step beyond Mickjoebill's suggestion: design a light-weight, multi-liquid, standby fire extinguisher bottle with extendible atomising wand. Have one that will run on wine (I'm not kidding), beer, water, milk (ahem pee) and any other non-flammable liquid. It's use is to act as a backup to the main extinguishers. If made of plastic in a concertina form it won't weigh too much, and will allow fire-fighting to carry on (or start) divorced from the standard, required fit, extinguishers. It will also be useful in non-aviation scenarios.