I always feed live and have only once had a problem with the snake getting bit and it was partially my own fault. I placed the rat too close to the snake in the enclosure, but it wasn't near his head.
As long as you are smart about feedin live by prescenting, and placing the rat on the opposite end of the enclosure you should be able to do it pretty safely. I feed in a 40qt tub and usually I take the cool hide out to open up a little more space for the snake to work with.
If you are nervous about the first time, start with a small meal to build up the snakes confidence.
The other idea that I have had (but never tried) is that you could put the rat in a pillowcase and spin it around a bunch. Now you have a disoriented rat (but still live). That would be an easy way to do the switch. Do a few disoriented rats then when your snake is a pro at eating those you could stop spinning em. Again this has not been tested by myself but it seems like a good idea to me.