Then with a web browser login to your LJ installation, and visit /admin/console. Run "set stylesys s2". I now see my journal running with the s2 port of the "generator" style.
I haven't figured out how to modify which style you use directly ("set s2_style xx" doesn't work because it's lacking a setter?) but you can change the $DEFAULT_STYLE set in your ~/cgi-bin/ljconfig.pl (copy the one in ljdefaults.pl to start with) to change it.
...Any comments from Brad? :)