Hehe, thanks for letting me have this one Martin...
Take 1/8" or 3/8" plastic line, carefully all on the same side of the line, puncture it with a pin. Run the line over your Vivarium, and insert a plug into the end of the line. Use a repti-flow 200 or 300 submersible water pump (or something similar) to pump water through the line, at first, the fast flowing water won't fall through the holes, but once it hits the plug at the end of the line, the water "pressurizes" in the line, and is forced out the small pin holes in a very fine mist.