I have done it before with an earlier version of rails eg :
Rails::Generator::Scripts::Generate.new.run(['model',@name])
but I am not sure of the command in Rails 3, and the 'require' statements to ensure I won't get any 'no such file errors'.
There is plenty of documentation on how to create a generator but not the more basic step of how to run the existing ones,
I don't know exactly how generators have changed but I'm curious - why would you want your app to be running generators on itself at runtime ?
Fred