Some software can not be installed on the master image computer because it needs to be uniquely installed on each clone.  So rather then have to copy packages to each clone after imaging, why not put the packages in a known location and then call the installer remotely using the command like:

installer -pkg /Users/labadmin/Desktop/post/Sophos_10.mpkg -target /

See the complete man page at:

https://developer.apple.com/library/mac/documentation/darwin/reference/manpages/man8/installer.8.html