We currently are feeding live to Hera and Eden and the main thing that I do is I gauge the rat's behavior. I pick them up by the tail with my feeding tongs (so I don't get bit, rodent bites hurt!) and if they are very eager to attack the tongs then I do a quick prekill.
The way I do it is a fast hard smack against a wall, that kills them instantly but they still kick a bit so if I get them in front of the snake fast they take it anyways. If the rat is more or less calm then I place them in the tank with the snake but I ALWAYS have the rodent in the tongs. That way I can control the rat a bit and if they get too close to bite the snake I already have the tongs in my hand.