I know of a place, a recovery and transport yard actually, and their big workshop has a massive space heater with ducted outlets at both ends, and is designed to run on heating oil/kerosene, call it what you like,
however, they hardly ever buy any fuel for it, as they use the pumped out fuel from cars that have had the wrong petrol or diesel put in at the petrol station,
not sure if they even bother to mix it a certain way, but once they have pumped out the cars tank into a container, the whole lot, petrol or diesel just goes into their heating oil tank, so cost them next to nothing to run, and has run perfeftly fine for years.
is there a recovery yard you could get a deal with? there is nothing else to do with it, as seperation is possible, but costly, and a fair bit of hassle too, they might be glad to see the back of it?
plus, the old school heater like the one i mentioned don't cost much either, Bonus!