i forgot to tell that the camera may miss the light of the flash if scene is well lit. generally it doesn't miss in lower light.
btw i didn't deeply understand your question, only i tried to guess what you may need
it would be nice to know what camera you got 
if you need rear curtain flash on a camera without such option maybe you got luck,
because evawr added rear curtain flash sync for a570 & sx100is a few weeks ago