Helper:
def add_interface_link(name,locals)
    link_to_function name do |page|
      page.insert_html :bottom, :interfaces, :partial => 'interface', :locals => locals, :object => Interface.new
    end
end

View:
#interfaces
  = render :partial => 'interface', :locals => {:f => f, :interfaces => @interfaces }

  %p= add_interface_link("Add Interface",{:f => f, :interfaces => @interfaces})

Partial interface:
.interface
  - f.fields_for(:interfaces) do |fi|
    = fi.label :name, "Interface Name :"
    = fi.text_field :name
    %br
    = fi.label :address
    = fi.text_area :address, :rows => 1
    %br
    = fi.label :mac
    = fi.text_area :mac, :rows => 1
    %br
    = fi.label :services
    = fi.text_area :services, :rows => 1