Conditionally disable workflows

I added a workflow to the layer actions of the layer list. Now I would like to have the menu item to be enabled only for actual data layers, and not for grouplayers or mapservices. 

The workflow already checks for the type of layer and returns immediately, but it would be nicer if the menu item itself was disabled when not applicable.

The most generic way would be the ability to set a ‘can-execute’ option in the designer, where a separate workflow can be set which determines whether the first workflow can be called. But an extention to the visibility filters based on the menu item's context would probably also work.