Why not use the clamp on variety of cable stop?
http://www.ebay.com/itm/suntour-clamp-on-downtube-cable-stop-guide-for-bar-end-shifter-barcons-NOS-/262511381270?hash=item3d1ee5cb16:g:XaQAAOSwZ1BXe1n1
http://www.niagaracycle.com/categories/origin8-clamp-on-frame-cable-stop-double-34-9mm-silver?gclid=CKiO5Zvc3s0CFQKTaQodjYEPTA
http://problemsolversbike.com/products/backstop