XDCR replication initiated by secondary cluster

We’re evaluating whether we can use Couchbase to replace our proprietary synchronization technology. As far as I can find, it seems that bi-directional cross-data center replication (XDCR) requires each side to push their changes to the other cluster. But what we need is that a secondary cluster will push and pull the changes to and from the primary cluster, without the need for the primary to connect back to the secondary. Our secondary data centers are not reachable from the outside, since they are deployed in remote locations. Is this possible at all?