skip send invitation

user.rb

class User < ActiveRecord::Base
  has_many :group_memberships, :dependent => :destroy
  has_many :groups, :through => :group_memberships
  attr_accessor :skip_invitation

  devise :invitable, :database_authenticatable, :registerable,
         :recoverable, :rememberable, :validatable

  protected
  def deliver_invitation
    super unless skip_invitation
  end
end

users_controller.rb

@group = Group.find_by_name('foo')
@user = User.invite! do |user|
  user.skip_invitation = true
  @group.members << user
end
GroupMailer.welcome_invitation(@group, @user).deliver