I feed in a seperate tub. I only wait until the snake is done eating and then, very carefully, put him back in his cage. Usually I see the following sequence to let me know he's done:

1) Mouse quits traveling farther down. It usually stops just past halfway. At this point you can see the swallowing action of the muscles along the body stop.
2) Jaw reset. (yawning action)
3) Resume movement and/or tounge flickering. This can either be him sniffing around to see if there is another mouse or it can be him trying to escape. Either way, there is a point where he starts to act more "normal".

Also, I'm especially careful to approach the snake from behind the head when taking him back out as he's still a bit torqued up. But, he knows the routine so he's never even looked about to strike.

I also always heavily mist the cage before putting him back in. (He likes fresh droplets). I've found he usually takes a post-meal drink to wash that furry thing down.