Sue it is best and safest for your snake to not restrain the mouse at all. Simply put the mouse in the enclosure as far away from your snake as possible. That gives your snake time to set up it's strike properly. The mouse may stay still or wander over to the snake (captive bred rodents have almost no idea what a predator is). The snake may go to the mouse or stay in an ambush position and wait it out. This is all normal prey/predator behaviour.

When you restrain a living prey item you can make it frantic. A frantic rodent is more dangerous to your snake and far more likely to bite the first thing it sees.

If it helps you feel better about this very natural process remember snakes were designed by nature to eat rodents, rodents are part of a very well designed food chain. You are really just a cog in a wheel dear that's been turning long before you were born and will continue to turn long after we're all dust. As well, the act of constriction by a snake is likely one of the quickest and most humane deaths. It is not suffocation, it's the almost immediate stopping of heart function (much like a human dropping dead of a massive heart attack without warning).

It's not always easy to feed live, but if you do so with respect to both predator and prey and knowledge of how to do it safely as well as understanding of the snake/rodent relationship...it will be fine.