A lot of folks seem to warm up the prey with a hair dryer (after it's fully defrosted) to make it warm enough to simulate life I guess. We feed pre-killed right now so that isn't an issue for us.
We've just switched to a loose substrate from newspaper and will just put down a layer of newspaper right over the substrate when we feed then after the snake is done and not in hunt mode anymore we'll just take that pad of newspaper out. That should ensure the snakes don't get any bedding in with the mouse/rat.
I don't know about your snake but ours come barrelling out of their hides when they smell dinner. Half the time we can barely get the prey in on the hemostats before it's grabbed up. For us, feeding in their own enclosures is working great!
~~Jo~~