[xmonad] Restricting mouse wheel bindings to a particular window

I've just started digging into xmonad a bit and it seems pretty cool, but there's one thing I haven't been able to figure out thus far. In wmii I have a pretty nifty setup where I can use the mouse wheel on the bar at the bottom of the screen to switch tags (workspaces in xmonad terminology). In browsing through people's configs on the haskell wiki I found some that have mouse wheel bindings, but they all seem to use a modifier in combination with the mouse wheel. What I would like to do is detect whether the mouse wheel event occurs in a particular window (dzen for example) and then do something based on that event (eg switch workspaces). Anyone have any ideas? Is this even possible? Thanks in advance. David Whittington