The fuel you put in the tanks only costs you what is costs to carry it if it is still in the tanks when you land!!!!! = bugger all. That 150 kgs costs 3kgs per hour to carry - thats all. It would cost $195 whether you put it in the tanks at a or b (+/- cost differential).
Most sensible recent comment in my view. This cannot be the best way of achieving cost savings by reducing overall wieght of the aircraft at take-off. The bean-counters might as well insist on all passengers going to the toilet at the gate!