guest_box_cell.rb

class CurrentUser::GuestBoxCell < CurrentUser::ProfileBoxCell
end

profile_box_cell.rb

class CurrentUser::ProfileBoxCell < Cell::Rails
  helper FrontHelper
  helper SessionsHelper
  helper UsersHelper

  build do |opts|
    CurrentUser::GuestBoxCell unless logged_in?
  end

  def show
    @user = parent_controller.current_user
    render
  end
end

show(guest).html.erb

<ul id="guest_links">
  <li><%= hop_on_board_link %></li>
</ul>

show(profile).html.erb

<ul id="current_user_links">
  <li class="welcome">Welcome <%= link_to_user  @user %></li>
  <li><%= logout_link %></li>
</ul>