module ApplicationHelper
  def add_interface_link(name)
    link_to_function name do |page|
      page.insert_html :bottom, :interfaces, :partial => 'interface', :locals => {:f => f, :interfaces => @interfaces }, :object => Interface.new
    end
  end
end

View:
%p= add_interface_link("Add Interface")
#interfaces
	= render :partial => 'interface', :locals => {:f => f, :interfaces => @interfaces }