A 1 tank "conversion" in any climate at any time of the year is a horrible idea, it is harmful to your engine and it is just plain lazy!

You have two options:
1- Use a two-tank system.
2- Convert the illegal fuel into BioDiesel.

Why ruin a good car with grease? Its a filthy fad, its illegal, its harmful to your engine, it takes taxes away from maintaining the roads, it increases NOx emissions, it does nothing to alter global warming, it has no impact on our oil use and it destroys the value of an otherwise good car.