Cloud-Storage has become part of the standard toolkit for enterprise-grade computing. While being cost- and energy-efficient, cloud storage's availability and data confidentiality can be problematic. A common approach of mitigating those issues are cloud-of-cloud solutions. Another challenge is the integration of such a solution into existing legacy systems. This paper introduces the Archistar Backup Proxy which allows integration of multi-cloud storage into existing legacy enterprise computing landscapes by overloading the industry-standard Amazon S3 protocol. The paper provides multiple lessons-learned during implementation and concludes with a performance evaluation with traditional backup solutions utilizing redundant remote storage.