This has been reported as a defect and can be found in
TEC525328
It also mentions the approach Federico gives, to drive this via GEL by making sequential calls to XOG out individual project's documents.
You would not need any external batch files though, GEL is capable of taking a XOG template, modifying attributes/data within it, and making a XOG request upon each one itself through the soap:invoke tag. It might be easier or better managed either way.
If you can, please log a support issue on this to say that the defect CLRT-50875 has affected you. Thanks.