Assuming the mouse is an appropriate size for him (about the same girth as the fattest part of your snake's body), I'd chalk this one up to him being a little stressed still and put him back in his regular enclosure. Leave him there (and don't mess with him) for the next week. Don't handle him, try to feed him, etc. Pretty much the only thing you'll be doing is making sure your husbandry (temps and humidity mostly) is dialed in, ensuring he has clean water, and cleaning up any messes he might make. Then, in a week, try feeding him in his regular enclosure. There's no reason to feed in a separate enclosure (for many reasons). Let us know how it goes!

Best regards,
Eric