Upgrading Rails and locking – grande finale?

I think I finally found way to snap to older Rails version in shared environment. Current (with Rails 1.1.2) way is to add to config/envrionment.rb following line in the beginning:

RAILS_GEM_VERSION = '1.0.0'

and run rake rails:update in order to update config/boot.rb. Of course if You want to use older Ruby on Rails version, it need to be installed on shared host :)