Playback control

Hi All,
I've looked and looked, but come up empty handed. What I'd like to be able to do is have the physical playbacks control whatever playback bar is currently selected. In essence, the same as clicking the "dock" button. But without having to unhide the dock button, and physically click on it. I guess you could say I want to "auto-dock" the currently selected playback bar. Is this there and I'm just missing it?
Thanks!