The Ideal

Using rvm, it would be awesome to be able to have multiple Rubies on one webserver, and through some sort of server configuration, be able to assign Ruby versions to different Rails/Sinatra/etc apps on a per-project basis.

I am aware, from rvm's documentation, that Passenger only works with one Ruby at a time. :(

The Compromise

Failing that, it would be nice to at least be able to concoct a way to be able to assign projects to a Ruby 1.8 or a Ruby 1.9 interpreter. I've read that using Nginx as a reverse proxy allows running Apache and Nginx on the same box. Would it then be possible to have Apache+Passenger using one Ruby, and Nginx+Passenger using a different one? Maybe use something other than Passenger with Nginx?

Am I Barking Up the Wrong Tree?

Am I missing a good solution to this issue? Am I walking into a nightmare configuration situation? Is what I want even viable, or is it necessary to run another box to run a separate Ruby version?