I Agree on the additional cost and effort required but the cleanest and recommended approach would be to move all the assets into S3, perform cleanup there and then use Bulk Import to move assets into AEMaaCS. This will require least amount of development effort. Also Bulk Importer ingest assets as-...

Have you looked using SAML Authentication to establish SSO with CA SiteMinder. Required configuration for SAML Authentication has been documented here:https://helpx.adobe.com/experience-manager/kb/saml-demo.htmlhttp://docs.adobe.com/docs/en/cq/current/core/administering/saml-2-0-authenticationhandle...