you can use clean vegitable oil if it is heated, most people run 2 fuel systems, they start the truck on #2, run it for a minute or 2, the water from the radiator runs through some copper type tubing in the tank full of veggie oil and heats it and thins it, once the veggie oil is ready you switch fuel systems, and the truck runs fine on the veggie oil, you have to make sure the fuel filter on the veggie oil stays clean because if you loose fuel pressure to the injectors stuff starts to go bad... when you want to shut the truck off you switch back to #2 to clean out the veggie oil from the injectors and fuel lines so it will start when you get back to it.
there are some new systems that use electric fuel line heaters to heat the veggie oil as it passes through the line and as it goes into the fuel pump, it works well you just have to activate the sytem before you turn the truck on if you plan to fire up on veggie oil.
you cannot just mix the veggie oil in your fuel like an additive, it wont mix well and stuff will clog, thats what the bio diesel is about, its a conversion to make the veggie oil into a fuel with a similar consistency to #2, you mix it with your #2 and it runs great, it is slightly thicker than #2 so thats where the worries come from about running higher than 50/50, and you can set up and make the stuff at your home. if i remember right you can make the fuel for something like under a dollar a gallon, but of course you should mix your new fuel with 50% #2 to run it in your truck...