This might be way off, but if you don't have a startup file try using the example one listed here. I think you may need to load the Apache2 module and ModPerl::Registry... maybe some of the others, but I'm not positive. I'm not a mod_perl expert, but I did manage to get it working on my server a few months ago.
mentioned mod_perl2 doesnt use Apache::Registry. It uses ModPerl::Registry.