Just run a rake task without having to setup a special capistrano task.

Usage

cap rake:invoke COMMAND="db:migrate" #yes, its a silly example...

Setup

namespace :rake do
  task :invoke do
    if ENV['COMMAND'].to_s.strip == ''
      puts "USAGE:   cap rake:invoke COMMAND='db:migrate'"
    else
      run "cd #{current_path} && RAILS_ENV=production sudo rake #{ENV['COMMAND']}"
    end
  end
end