Hi Mick,
You can edit the xml file to do this, full instructions are in section 4.3 of the admin guide - located here https://websmp201.sap-ag.de/~sapidb/012002523100019802842015E/14SP15_aaoffice_admin_en.pdf (S number required)
Summry of this is below
The BoeConnection setting allows you to define a system connection to the business intelligence platform. It is maintained by an XML file which is stored in the file system under %APPDATA%\SAP AG\SAP BusinessObjects Advanced Analysis\Settings\BOESettings\BOESystems.xml