Well that problem isn't project-breaking. You get a container used for storing gaseous hydrogen, H2, and like the one they have at
Http://www.unitednuclear.com all you have to do it basically intravenously connect the fuel line from the hydrogen tank to the fuel line right before the FIS but after the pump and have a computer chip controlling when to heat the tank and release more/less H2 (see the webpage and go to research and development on the top of the page for info on their hydrogen conversion techniques, not very much detailed info but they solve quite a few problems)
Oil and gasoline could then be added to the ordinary gas tank and you could use a ratio instead of 100% gas or 100% H2. that way you could even run on like 10% gas/oil (which could be 50/50 to compensate lubrication) and 90% H2.
Never tell someone that something is impossible, you just need a little imagination and creativity and anything really does become possible.