Retention policy for subsites

Rather than deleting SharePoint Online sites, I move them to a subsite of a site collection called Archive where they can stay in three years until they are deleted. I want to leverage Retention Policies for this purpose so that sites are automatically deleted after three years. I can easily create a policy for the site collection, but I wonder if it is possible to specify that subsites are to be deleted three years after they have been created without having to add individual sites to the policy every time I archive a site?