Windows 7's KB 2852386 update, "Update is available that enables you to delete outdated Windows updates by using a new option in the Disk Cleanup wizard in Windows 7 SP1", now allows Disk Cleanup to clean up the WinSxS folder. From KB 2852386's Knowledge Article page:
This article describes an update for the Disk Cleanup wizard in
Windows 7 Service Pack 1 (SP1).
This update adds a new plugin to the Disk Cleanup wizard. After you
install this update, you can use the Windows Update Cleanup option to
delete Windows updates that you no longer need.
- The Windows Update Cleanup option is available only when the Disk Cleanup wizard detects Windows updates that you do not need on the
- To enable you to roll back to previous updates, updates are stored in the WinSxS store even after they are superseded by later updates.
Therefore, after you run the Disk Cleanup wizard, you may be unable to
roll back to a superseded update. If you want to roll back to a
superseded update that the Disk Cleanup wizard deletes, you can
manually install the update.
More info at KB 2852386's Knowledge Article page