Feeding in the enclosure induces aggression in snakes is a common MYTH.
Whether or not you feed in the tank or in a separate tub, if you feel uncomfortable with picking up your snake you can use a rolled up newspaper or paper towel roll to direct his head away from your hand. It doesn't hurt the snake and you'll feel more reassured. Also wash your hands before handling your snake. You might smell like food or some other type of animal that gets him interested in your hand.
Here's a thread you can read: http://ball-pythons.net/forums/showt...ight=feed+tank
I'll say that the majority, if not everyone, in that thread who feeds in the enclosure has not seen any behavior change in regard to aggression.
I feed all of my snakes in their enclosure and have not seen any developed aggression either. Also an animal who is in shed may react defensively to a hand, just in case yours is going into shed.
Edit: Also I tend to find that transferring a snake back and forth between tank and feeding bin stresses the animals out. Feeding in the enclosure minimizes that stress. Although there are exceptions to this.