I was thinking the same thing Snooker....but I wonder what effect the lights would have on the drag of the boat. I would think that a remote light (such as what TGF has) would be better. I would be scared to install Ocean LEDs or anything on the keel of a plastic kayak due to the insufficient support of it from flexing, bending, etc with either temperature or structure contact. Therefore, drilling a hole in the bottom of the boat doesn't sound like fun to me.
Maybe one option is, find some small LEDs that might fit through the scupper holes that you could just feed through if you're wanting to do something like that. You may not even need to snake them through as the reflection from the light within the scupper may produce enough to get bait fish swarmin' around you.
Otherwise, you could go for a no hole mounting method like Maybe Marine Goop to practically glue them to the hull, but then you have wires running all over, etc.
Plasma LED sells a Marine LED light for $19.99 which has a 4.5cm front with a 3cm base (equals approx 1 3/16") which may fit into a scupper. Not sure how big the scupper holes are.
Just my $.02