Exchange 2010 retention policy tag to address unread emails

Is there a way to use retention policies to delete unread email older then a certain age?

We have over 350 users and a large sum of them have mailboxes with 50% unread emails. We are using the new online archive folder in 2010, so we can now longer use managed folders and inbox rules to move unread email to a special folder that is set to delete its items older then 60 days. And of course, we don't want to archive unread messages.

We have shown that we could reduce our databases by 1/3 simply by deleting unread email.

I have had no success using the New-RetentionPolicyTag -ManagedFolderUpgrade to convert our managed folder policies.

Can someone pleace help, or at least let us know if this is even possible.