I had help on a similar issue.

I think what you want to do is map the play and menu button in the 'default behaviours' setting under the 'Mappings' section on preferences.

I found out today that this controls just the button press when i) in Finder and ii) the button isn't required in current app.

Likely play and menu will be used by whatever app you launch, so you won't need to set anything else up beyond that.

Here's my 'default' behaviour for 'menu' mapped to open Plex:

https://dl.dropbox.com/u/343477/ofy89QYYAxCidW/rb-plex/rb-default-bh.png

As soon as Plex (or other apps) are running, the menu press is given over to the running app.