You've got a chance of some rats for him? Cool! Depends on the size of the rat - a royal of any size can eat rats but the rat should weigh around 10/15% of his bodyweight or you can feed a rat whose girth is no larger than Blitz's.
If your going to feed live it may be worth having a quick watch of this video http://youtu.be/gFB3Pa1SDhs However you could dispatech the rats yourself before hand if you need to.