Have you ever had to re-attach a Sharepoint workflow after it has been removed?
It is impossible via the browser (from what I can see) and via designer it is far from obvious how to accomplish this. What you need to do is open the workflow in Sharepoint Designer, click “Finish” and the workflow will re-attach itself. Not very obvious, but it works.
Unfortunately there is no way to associate a workflow with another list unless you open the various workflow xml files change the list guids inside.