Anyways. I got RVM installed systemwide. That wasn't too bad.
But when I tried to get Passenger to install (with rvmsudo passenger-install-apache2-module), I got:
Your RVM wrapper scripts are too old. Please update them first by running 'rvm update --head && rvm reload && rvm repair all'.
First off, rvm update --head has been removed. I believe it's been replaced with "rvm get head" or even "rvm get latest". I ran "sudo rvm get latest". It did stuff. I'm pretty sure I was already at the latest though. Ran sudo rvm reload and sudo rvm repair all. Then tried rvmsudo passenger-install-apache2-module again. Still didn't work.
Tried sudo passenger-install-apache2-module. That failed - got:
Tried passenger-install-apache2-module in userspace. It worked, surprisingly, but then it hit permission problems as it tried to write to various directories.
In the end, I did sudo irb, then manually ran each line in passenger-install-apache2-module, and that worked perfectly.
I don't know if Passenger will work when installed that way; I'm modifying my apache config now, but I'm at my train station...