Now I'm still convinced that this dead fly was only playing dead to trick me and flew away once I had got bored of waiting for the clutches of my trap to close.
But low and behold when I returned to my potted plant the corpse was gone! So one could believe Mr Fly was gobbled up. I have been on the look out for more dead flys to fed my little green friend. Will update if further tests prove successful, although I have read online (reliable source) that he only needs one or to bugs each month.