Solution:

A simple wooden box section tube with a servo actuated door at each end and a IR LED sensor in the middle. The idea is that the 'trap' is placed in a known mouse 'highway' (behind the fridge seems to be the best); mouse scurries through the tunnel (which is open at both ends), trips the IR sensor, which activates the servos to snap the doors at each end shut. The device then emails you to let you know that there is a mouse ready for relocation; and continues to send an email every hour to remind you that you still haven't released the mouse.