bfeley,
I'm going to go out on a limb and say, "No, there is no way to install multiple Java plug-ins for one running version of Mozilla".
While you can install a symlink in the plugins directory of your Moz install by linking to the file <libjavaplugin_oji.so> in your particular java install versions, it appears that Moz will only recognize one java plugin at a time. Maybe, you could make multiple Moz installs, each with a link pointing to the different JRE plugin version you need, but that seems kinds of dumb.
If there is a way, I would like know as well, as it seems we both have similar requirements (1.3.1 and CiscoWorks).
Good luck,
Edwin