Here's an idea:
Get hold of one of these for each person: http://www.ebay.co.uk/itm/Mini-Handheld-Pistol-Grip-Megaphone-Loud-Speaker-Bull-Horn-Voice-Amplifier-Siren-/400483692469?pt=UK_MusicalInstruments_Other_Pro_Audio_Equipment&hash=item5d3eb02fb5
£8.99 each. And sing our hearts out. I'm...