That is correct,
You can only add and remove enterprises and edit the list of partner applications remotly and 3PDS is basicaly unusable unless an enterprise is added. If you have administrative rights to Intel AMT, you can use Intel AMT Commander to add a new enterprise and edit the partner list. Once done, you can use Intel AMT Outpost or your own tool to access 3PDS localy.
Ylian (Intel AMT Blog)