Initially I inserted cotter pins horizontally but they started to wear so I took Matts advice with my own revision. I found a great glue at West Marine. "G/flex (2 part)epoxy 650-8a and 650-8b. Made for kayaks. First I drilled a small hole at the BOTTOM of each female cavity. Remove the screws that hold the pegs to the seat and replace them with longer machine type screws that will extend through the hole out the bottom of the cavity. Secure them in place with washers and nuts/wing nuts etc. But pour the glue into the cavity first! In the unlikely event the glue should break down(over time) from the elements- the screws will still hold. The seat has stayed nice and tight after several really rough rides. West Marine also has a great glue for the carbon fiber mast should you chip it.101-TS(2 part epoxy).
Good luck!Nothing more annoying than having those pegs pop out at a critical time.