How do I add a flash fire effect to a photo?
The infamous Deke just posted a Top-40 tutorial that does something that might work for you.
Have patience, the tutorial is about something else. But about half way in he adds a "splash" layer. Basically, he fired a flash into a mirror and overlayed that image on another and blended it in.
Here is another one where the author shows a way to add a "starburst" effect.