PosgtresSQL master-slave synchronous replication to multiple slaves

PostgresSQL has support for master-slave replication, but the synchronous
streaming replication
<http://www.postgresql.org/docs/current/static/warm-standby.html#SYNCHRONOUS-REPLICATION>
only supports a single synchronous slaves. You can have multiple slaves,
but only one will be synchronously updated the others being eventually
consistent.

Synchronous replication offers the ability to confirm that all changes made
by a transaction have been transferred to one synchronous standby server.
This extends the standard level of durability offered by a transaction
commit. This level of protection is referred to as 2-safe replication in
computer science theory.

If you run a large enterprise system in a master-slave replication scheme
on top of PostgreSQL, what options do I have for enabling multiple
synchronous slaves? Has anyone been able to set-up such replication
configuration?
Original SQL question:

http://stackoverflow.com/questions/23954844/posgtressql-master-slave-synchronous-replication-to-multiple-slaves