In lime and fertilizing spreading operations some operators have installed airborne refuel capabilities on their spread bucket.
The system works in the way that when you come in over the rig and change spread bucket the new bucket have a small fuel tank that fills into the helicopter fuel tank. So the system refills the helicopter tank during the short flight to spead the lime/fertilizer.
It is just a small amount of fuel on each bucket, but the system allows the helicopter to fly at minimum fuel all the time and thereby increase lift capasity. The time-in-air limiting factor will be the pilot, toilet, coffe or food. Maybe in an other order
I have seen this system on Bell 205 and AS 350.
CB