I asked Aero Tec Laboratories, Inc. ( ATL http://www.atlinc.com/rangeextender.html) about plumbing the bladder directly to twin outbards and received this response:

"For gasoline applications you may either siphon the fuel to the main tank, pump it with a manual transfer pump or connect the engines to run directly off of the bladder. "

My question,.... Has anyone ever tried this?