The next time I have any to dispatch I will see if I can get some video.
I use a ribbed silicone mat, It grips them and they cannot squirm. I lay them on the mat I use a sharpening steel and roll up their neck toward their head, while pulling on the base of the tail, It is done is like 1 second.
They do continue to twitch afterwards, and that is a bit disconcerting, But they are already gone by that point. and it makes the ferrets a bit more interested in them not like they need to be any more interested in them.
That did seem quite humane. I don't feed whole prey but if I did I would be able to do the chamber over cervical dislocation for sure. Good job on your setup and your mindfulness of the cute little mouse.