Workflows

I would like a Workflow Rule to be activated only when a defined Stage in Potentials is selected. This Stage will never be selected when a Potential is created so I can not choose that option. I do not want the Workflow to be restarted every time the Potential is edited and the defined Stage is still selected.

1) User edits Potential and changes Stage to the defined Stage.
2) User saves record after editing.
3) Workflow Rule is activated.
4) User edits the Potential without changing the defined Stage which is still selected from step 1 above.
5) User saves record after editing.
4) The Workflow Rule is NOT activated again.

Is there a way to do this now? If not, I would like to request this feature.