You will need
victor mouse trap
and thin wire, sewing string or fishing line. I used dental floss so that you can see it in the pictures.
Step 1: Assembly
Make a loop with the thread.
Run the loop through the copper bar and set the trap. You set the mouse trap like you would normally except that you have the loop running through the bar.
Carefully and gently run the string to the other side. Tape the other side. Be gentle, it only takes a couple pounds of force to trip this.