ruby script/plugin install http://opensvn.csie.org/hidden_field_session/trunk/hidden_field_session/

Usage #1 (enables over the application )

class ApplicationController
   include HiddenFieldSession
end

Usage #2 ( enables only specific controller )

class YourController < ApplicationController
   include HiddenFieldSession
end

Usage #3 ( you can disable this feature)

class DisabledController < EnabledController
   disable_hidden_field_session
end

There is currently no advanced documentation for this plugin.