I'm having the exact same problem in DW CS5 now. Did you find a solution? Hitting fn+F8 isn't going to work on my iMac extended keyboard. F8 is the iTunes play pause button. Besides, having to command-tab to an app THEN hit fn+F8 just isn't going to work obviously.
I can't believe in 2010 this is broken.
Please do let me know if you found a way around it. I tried all the different layout prefabs in CS5, and without exception they all do it.