[Striiker]

One possibility is to FD behind the NPC and then open the hand-in window. Sneak and stand up. Click to hand in. This may help. I do a similar thing in SolA with the Goblin Merchant. I can't open a Sell window with him while FD so I FD behind, Sneak, stand up and open merchant window and immediately FD (since he turns around to face you typically). My thought is that if you have the hand-in window open already and stand while sneaking, you are indifferent. The hand-in may work. I'd test this with a lesser quest first.