Rails 3 upgrade - Custom cache store

I had a custom cache store set up in Rails 2.3. I'm in the process of
upgrading to rails 3, but have run into a snag. Before I had all the
setting in my environment.rb. It would basically load a yaml file
with my server settings, and set up the store via config.cache_store.
It seemed like the correct place for this in Rails 3 was as an
initializer. So I did basically the same thing, except using
MyApp::Application.config.cache_store. I don't get any errors, but
when the app loads, Rails.cache returns

Another interesting thing is that if I load it in application.rb, it
will return the custom cache_store. Hower, this doesn't work well for
me because Its dependent on things like Rails.env and Rails.root which
aren't initialized yet. Any help?