After the colon ( : ) is the salt! If you have the salt in a separate file, the only things you could do is either combine each hash w/ every salt or use -e.... BUT: the -e option w/ SMF hashes was *not* supported so far... this feature is *new* in cpu hashcat 0.46! See trac ticket above ^.
So either wait for the release or stick to option 1 (combine each hash w/ each salt yourself).
So either wait for the release or stick to option 1 (combine each hash w/ each salt yourself).