Custom data in afterRender method on initial load is always null

I see that the Scheduler returns custom data in the Update(data) function on the initial page load, but it doesn't seem that the Calendar works the same. I can return data on an update, but not on an initial load.

Has this feature not been implemented for the Calendar, or am I missing something? I just downloaded the newest Pro version 7.9.3373.

Thanks,
Brian Dick