Looks like what I was missing was one line.
modify sys folder /Common/datacenter-sync traffic-group non-default
modify sys folder /Common/datacenter-sync traffic-group none
modify sys folder /Common/datacenter-sync device-group datacenter-sync-devgroup
With these line you can create a folder under the Common partition, decouple that folder from the traffic group, assign it to another device group that can have your other datacenter devices as members and move objects into it for cross site synchronization.
to enable the object move feature
modify /sys db mcpd.mvenabled value true
and then you can do things like
mv ltm rule /Common/irule_that_can_be_used_anywhere to-folder /Common/datacenter-sync
mv ltm profile /Common/your_default_tcp_profile to-folder /Common/datacenter-sync