well, if hydrogen fuel enrichment is only good for cutting idle fuel consumption in half (
source), I have a much simpler and infinitely more effective solution. Turn off your dang engine INSTEAD of idling.
lean burn does help, but it is not the ultimate solution, it is a band-aid for an over sized engine. bsfc naturally peaks around stoich because you aren't passing unburnt fuel (rich) or pumping unused air (lean).