Is there a way to automatically append to $: variable in ruby to account for additional site_ruby locations?

Ruby is installed in /usr/local/ and using gem_install will properly install the new ruby files in to /usr/local/lib/ruby/site_ruby.

However there are some RPMs for ruby bindings to tools like shadow which we'd like to install and they install to /usr/lib/ruby/site_ruby (no local). Is there a standard way to tell ruby that this directory should also be included by default?

I know scripts could dynamically update $: or they could be called with -I but it seems like this is something that should be handled in the install.

Has anyone else found a clean way around this kind of problem?

thanks, chuck