I have an external pillar file:
-rwxr-xr-x  1 salt  staff  8038 May 22 16:21 /srv/pillar/cmd_lp.py

in /etc/salt/master I have
#pillar_roots:
#  base:
#    - /srv/pillar
ext_pillar:
  - cmd_lp: /srv/pillar/website-definitions.yml


And master shows this
2013-05-22 16:58:12,994 [salt.loader      ][DEBUG   ] loading pillar in ['/var/cache/salt/master/extmods/pillar', '/Users/salt/salt-environment/lib/python2.6/site-packages/salt/pillar']
2013-05-22 16:58:12,995 [salt.loader      ][DEBUG   ] Skipping /var/cache/salt/master/extmods/pillar, it is not a directory
2013-05-22 16:58:12,998 [salt.pillar      ][CRITICAL] Specified ext_pillar interface cmd_lp is unavailable