How Do I Use ExternalMouseWheel?

I apologize for the newbie question, but I'm trying to figure out how to initialize the ExternalMouseWheel helper to get mouse wheel zooming in Flex on the Mac.

I see that it requires the stage object and I've googled around for examples. I have a function set to receive the applicationComplete event but I'm not sure where to actually get the stage reference... it seems to be null.

Does someone have a working example?

thanks,
Pat