Galera cluster without having to specify all hosts on wsrep_cluster_address
EDIT:

My original answer below is still correct, but the is an easier way to handle this: multicast.  I didn't mention this before because I thought galera could only use multicast for replication, which is probably something else you probably want to configure to save bandwidth with a large number of nodes.  Basically, you can use a multicast address for the cluster connection in wsrep_cluster_address.  Using multicast will allow you to configure a single address on every node.  I'm using multicast for replicating data in my galera cluster, but unicast for the cluster connection.  The page I link to doesn't say anything explicitly about it, but you might need to configure a different multicast address for the galera data replication channel (gmcast.mcast_addr) and the cluster information channel (wsrep_cluster_address).  More information on using multicast with galera is available in a Percona blog post.

Original:

It is not required to have every node in the cluster defined in wsrep_cluster_address.  When a node starts up, it tries to connect to the provided addresses to connect to an existing cluster and then connect to all of the other current nodes in the cluster.  It only really needs to connect to a single node in the cluster to join since it connects to other nodes based on the current state of the cluster.  Because of that, if you specify a few nodes that should always be in the cluster, you should be fine even if there are many other nodes that are not specified.