WAL archiving from a standby backup strategy Postgresql 9.3
Postgresql provides a pg_receivexlog utility that can be used instead of archive_command to do wal log archiving. 

From the Documentation:


  pg_receivexlog is used to stream transaction log from a running PostgreSQL cluster. The transaction log is streamed using the streaming replication protocol, and is written to a local directory of files. This directory can be used as the archive location for doing a restore using point-in-time recovery