Set Collection Sync Flag via Plugin

I'm working on a plugin to keep folders and collections and sync, as I primarily work in folders and don't use collections.  I'm able to create paired collections for folders and keep add all of the photos to the right collections, but I can't figure out a way to set the "sync" to cloud flag for the collection - and it defaults to off.  Haven't been able to find anything in the SDK docs -- any ideas?