Add more than 6 lines on Polycom IP 650

I’ve been searching these forums and have not found an answer.

The Polycom IP 650 supports 3 sidecars, but only has 6 line keys on the main module.

The End Point Configuration Manager only allows 6 lines to be added to the phone. I would like to know if anyone knows a workaround to add more through the GUI. I know it should be able to be manually edit the phone configuration file in /tftpboot, but then any changes in the GUI would overwrite that file.

Has anyone ever done this before through the GUI with code modification?

After more research, it turns out that I need to use the attendant feature.