Oh boy. I have had more problems with this than anything. Having my snake take up to 3 hours to eat a rat. After many posts and trying everything I can I have learnt the following.
1) Doesnt matter how he eats it or how long it takes. If he is in a suitable enviroment to eat just let him be and he WILL figure it out eventually.
2) The only trick that I every found the worked is I feed F/T and it was to hold the rat by the tail for the strike and try to encourage him to strike near the head. Often where my snake bites is where he will try to eat from.