Tools for migrating GOS attachments

We're migrating data from a legacy SAP ECC system to a newly implemented one. Many SAP business objects, such as materials, maintenance plans, functional locations and FI documents, have documents attached to them via the Generic Object Services (GOS). The documents are stored in the legacy system's database.

What's the best way to migrate these GOS attachments along with the SAP business objects? Are there really no standard tools for that?

Note 389366 and KBA 2365781, as well as many Q&A posts describe how to use report RSIRPIRL to migrate the documents from one content repository to another. However, in that scenario the ECC system stays the same. If we migrate the attachments to an external content repository while the business objects are in the legacy system, can we somehow ensure the integrity of the links when we migrate to the new system?

For custom development scenarios, Philip Johnston posted a nice blog about uploading and downloading GOS attachments. In it's comments, he proposes using the tools for a migration scenario, too.

One post quoted an anonymous source: Migration of GOS attachements is challenging. Nothing ready for use exists in SAP to do it. '

Is that really the case?