Couple of things....
Is fuel costing segregated now for commercial vehicles?
Can you tell us, specifically, why adding a transport levy/duty/fee onto a product that has already landed on IOM soil can't be done? It's not rocket science or mathematical bollocks.
Why do so many of these issues get thrown into the "Hard to Do" tray? Might it be because the status quo is actually producing more revenue than the fairer alternative?