I use Jenkins to configure my multi-configuration project.
The Axes I use are:
Labels: Mac10.6, Mac10.7, and Windows
Platforms: Mac10.6, Mac10.7, WinXP, Win7, and WinServer2008
Tasks: App_Installer, App_Uninstaller, and so on
A matrix will be generated, and I intend to let the tasks from windows platforms go to execute on Windows machines(with Label "Windows"), by using a filter as (label=="Windows"&&(Platforms=="Win7"||Platforms=="WinXP"||Platforms=="WinServer2008")).
The matrix will be setup and the unconfigured nodes are gray out, however, it is clear that it makes no sense for the node "WinXP" to exist on label Mac10.6 and etc. Although it is shown as diabled/unconfigured/gray, I would prefer you can provide a choice to remove them from the UI.