I bought a pre-fab one from Stoddards and added it to a 4pc. back-up rod (8wt) I have. Its the kind with the screw on metal stud sticking out of the cork.
Drilled hole in bottom of reel seat cap, filled with epoxy, stuck in, and let dry. 4 years old and holds very well. Seem to make the rod a little bottom heavy as compaired to a rod designed with a butt - but not really noticable.