How to spawn recurrent events with custom field data from parent

I have a custom field for the incsub_event type called: "SoundCrew"
When I create a new recurring event and set this custom field with a value, the spawned recurring events' SoundCrew custom field is blank.

Programmatically, how do I ensure spawns are created with the custom field data of the parent?

(All code must always be upgrade safe!)