there is a way ..
You can create a batch file that
1) runs sja
2) next calls a zip program that can be executed from commandline. Filzip http://www.filzip.com is an excellent (free) one that has command-line option. You can add into an existing archive.
3) finally execute a 'del' command to delete the .sql file when zipping is done
it is a .bat with three lines. You can schedule the .bat and not the SJA itself then.