class User < ActiveRecord::Base
  acts_as_api
  api_accessible :only_names do |t|
    t.add :first_name
    t.add :last_name          
  end
  api_accessible :age_and_names, :extend => :only_names do |t|
    t.add :age
  end
end

class User < ActiveRecord::Base
  acts_as_api
  api_accessible :only_names do |t|
    t.add :first_name
    t.add :last_name          
  end
  api_accessible :age_and_first_name, :extend => :only_names do |t|
    t.add :age
    t.remove :last_name
  end
end