First, make sure that your configuration uses the same catalog backend than your distro. Then, you can set the bin and scripts variable in your config file.
Example:
bin=/opt/bacula/bin scripts=/opt/bacula/scripts
The ./scripts/prepare-other-loc will tweak your regress scripts to use new binary location. You will have to run make setup to be able to use regress binaries again.
$ ./scripts/prepare-other-loc $ ./tests/backup-bacula-test ...