As option you can try to use wsusmigrationexport.exe from C:\Program Files\Update Services 3.0 API Samples and Tools\WsusMigrate\WsusMigrationExport folder
on source WSUS
wsusmigrationexport.exe settings.xml
on destination WSUS
navigate to C:\Program Files\Update Services 3.0 API Samples and Tools\WsusMigrate\WsusMigrationImport folder. Run
wsusmigrationimport.exe \\path\settings.xml Approvals None
Maxim Sinel'nikov