I tried to build a quick sample that does this..
It has two scripts and uses a custom keyboard hotkey to stop the images flipping.
Run the scene from the sequencer and press F8 to stop the images and display a winner..
The flipping is controlled by a script on the scene director that hides/shows random images and has a loop event to jump back to the beginning.. The F8 key is defined in the keyboard mapping menu and runs a script that looks for a scene on Channel 1 Layer 0 and looks for a scenedirector track called "LoopTrack" and disables it (this stops the looping).
http://ross.brickftp.com/f/a4fae5a45
If you have different numbers of images you may need to edit the script on the scene director..
#XPression