Asynchronous Replication with Galera Cluster ?

My question is simple. Today i have a Galera Cluster with 3 nodes to write/read. And i want to put one(more to come) slave (asynchronous replication) to the cluster. As all my writes are located on 1 node, it's ok. But if i change the node on which the writes come... My slave is not synchronized anymore. I had to change the master of the slave to have the new written node as master. It seems that each galera node write only transactions from "real client" to replication binary log, not the ones from wsrep.

Is there a way that i can ask to a Galera cluster node to always write commited transaction on the replication binary log ? Even if the transaction come from wsrep and not "real client" ?

Thx in advance,

-- Nicolas Blanc.