I had to look it up online to see what you were talking about with the fuel pump nozzle being different. Are you talking about the rubber boot looking things that covers the nozzle like foreskin? They used to have things like that on the pumps way back in the 70's and removed them because they found that they were too expensive to maintain and caused more spills and drips than just the bare pumps did. Crazy that they brought them back.
Found this too.
http://www.millproprecisionmachining...uct/NZLBDY-200
Your funnel idea would keep the spills from going down the side of the truck, but then you'd have to drag that funnel around in the bed. It would never be clean, so more dust/debris would make it into your tank... but you say you'd wipe it out every time... and then when you're done pumping, you'd have to wipe it out again or gas drips would be in your bed. Seems like more of a pain in the rear to me.