I was peripherally involved with a similar programme when Bristow decided they needed it for a Puma operation in Australia. The equipment for refuelling in the hover is commercially available.
Flight Refuelling manufactured the manifold assembly that was installed on the airframe filler necks on the fwd and aft tanks. The idea was to winch up the hose, then fill both tanks through the single filler port. For the life of me, I can't remember if this was a gravity system, or a closed circuit - I seem to think it was a closed circuit system of some type.
They had sent someone up to measure the installation for the aircraft, and FR manufactured a really nice piece of equipment to install on the aircraft. There was only one minor glitch to the entire cunning plan, the measurements and planning for this great escapade had been accomplished on a Puma in heavies at ABZ. Due to the status of the inspection, the machine had no cabin doors installed, which also conveniently made everything so much more accessible. When the moment arrived to install the great invention, there was considerable embarrasment when it was discovered the cabin door could only be opened about 8 inches, due to the manifold being installed on the fwd filler neck.
Still, never ones to let minor problems interfere with our success, we continued to perform the flight testing portion with the poor winchman trying to manhandle the fuel nozzle and attach it all, through a rather small opening in the cabin door! We did fly-away and break-off tests with the line connected and various other fun things to pass the weekend away productively.
Although it did prove possible to refuel the aircraft in flight, the entire project quietly went away. As did an internal aux-tank (concept) for the Puma that was going on the same weekend, that involved an S58T aux tank stuffed in the tail supported on wooden trestles.
I actually have pictures of all this fun and games somewhere.
Perhaps the best one was the S76 ferry tank system that could neither get in or out of the aircraft doors. It sure looked nice assembled on the hangar floor though!
Ah, them was the days!