Thank you for your comment, I'm very interested in deployments of Ruby applications that come as close as possible to a single binary. Do you have any pointers to the mentioned folk knowledge that you can share?
But that's not the only way to do it; it's in keeping with the "uberbinary" idea to have a single tarred up directory and a known entry-point, such that once that's copied to the server you don't need anything else, no post-install build steps to get running. I built something to do everything-but-the-interpreter a while ago: https://github.com/regularfry/au.git.
The tricks that let these things work almost always boil down to knowing about the existence of a very few environment variables, and when in the build process you need them set to which values. `au` relies on $GEM_HOME, $GEM_PATH, and $PATH, and knowing what to do with $DESTDIR and `ruby-install` ought to get you a ruby interpreter as well (although `ruby-install` is just a shortcut to `make` in the MRI source). Where you'd look to learn that stuff now, I don't know.