It's actually mostly done.

To connect to your database, simply run:

ActiveRecord::Base.establish_connection(:adapter => 'sqlite3', :database => 'db/development.db')

Or, if you'd like to store your database config in a YAML file:

database_configurations = YAML::load(File.open('./db/config.yml'))

development_configuration = database_configurations['development']

ActiveRecord::Base.establish_connection(development_configuration)

To use the Active Record rake tasks, use this gem: https://github.com/rosenfeld/active_record_migrations. It also provides a rake task for generating migrations.

It would be great if that gem weren't needed - I think that's where the big opportunity for improvement is.