How to configure multiple hot standbys in Postgres?
Yes, it is possible.
I assume (based on you term "hot standby") that you are using streaming replication right now with your actual standby server.


For this you setup the master server with a pg_hba.conf allowing the slave to connect to the special database "replication". For the additional slave you need an additional entry (don't forget the reload)

# The standby server must connect with a user that has replication privileges.
# TYPE  DATABASE        USER            ADDRESS                 METHOD
  host  replication     replication     192.168.0.20/32         md5


The user "replication" is created by using psql:

$ CREATE ROLE replication WITH REPLICATION PASSWORD 'password' LOGIN


The configuration on the master should be there (wal_level = hot_standby and probably an activated archiving).

On the reporting-slave you just need a full backup and a valid recovery.conf. If you use pg_basebackup it can create a recovery.conf for you (see the blog entry https://www.depesz.com/2012/02/03/waiting-for-9-2-pg_basebackup-from-slave/).
Don't forget hot_standby = on to use the slave for read-only-queries.

You also can use the "old" slave as master for the reporting-slave (cascading replication).