A quick search has revealed nothing out of the box or third party available for this. However likely you could script something since there are plenty of API's that interact with Active Directory, you would have to:
1) Pull all information out of your Forms based provider (be it SQL Server, XML File, FaceBook, etc.)
2) One at a time, use the active directory API's to create new logins.
Sorry but I don't see an easier way here.
Also as far as advantages, you are using a proven method of securely storing logins that can be used elsewhere within windows with ease, such as Windows Login, SQL Server Login, Kerberos delegation, etc. But it's really apples vs. oranges going from FBA to AD.