Prevent Flash Games from running in MS Excel

This has been a security issue and has caused a major headache in our office. after blocking access to games installed by windows, streaming media from windows media player and AIM, now they are playing games through excel. There have been websites offering flash games that are embedded into excel files and its been hard trying to block it by disabling vba in office since there would be other documents in our office that would require it. does anyone know how to prevent users from executing these flash games in excel???