The custom layouts are not supported for CTMS. They apply to meetings scheduled on an 8510 bridge. The 8510 bridge supports only single screen endpoints (Tandberg as well as single screen endpoints from other vendors like Polycom). Please refer to the section Conference Layouts on page 78 of the attached document for more information on the layout IDs:

http://www.cisco.com/en/US/docs/telepresence/infrastructure/mcu/api_guide/MCU_API.pdf