How do I create multiple backup jobs using DejaDup backup service?
Deja Dup cannot do that at the moment, you are right. And it currently doesn't plan to (the feature request bug is marked Won't Fix).
I've heard good things about Back In Time, but haven't tried it myself.
Open deja-dup-preferences from terminal as a different user.
su -
or
su backupuser
deja-dup-preferences
Make the required source, destination and other settings. In Startup Applications Preferences of you general user, add below command to autobackup when you login to your general user.
sudo -u backupuser -s deja-dup --backup