def run_task_on_single_host
  Capistrano::Configuration::Roles.class_eval do
    yield
  end
end

if ENV['server']
  run_task_on_single_host do
    alias old_role role
    def role(which, *args)
      options = args.last.is_a?(Hash) ? args.pop : {}
      which = which.to_sym
      args.each do |host|
        next unless ENV['server'] == host
        roles[which] << ServerDefinition.new(host, options)
      end
    end
  end
end