video
This Mike Aronoff video discusses kayak outfitting and might be of some use to the OP.
http://www.youtube.com/watch?t=170&v=BPnBGTAzovo
The boat shown is a more modern recreational type kayak than the Riot Glide. The Glide, like nearly all whitewater kayaks, has vertical central foam pillars fore and aft to support the decks and reduce the likelihood of them collapsing and trapping the paddler. Recreational boats and sea kayaks usually lack them because the entrapment danger is much less.
Also, the Glide, like many whitewater boats of that vintage, lacks separate thigh braces. The forward deck itself serves as the thigh brace. But unless your legs happen to be identical to Corran Addison’s, for whom the boat was designed, you are probably going to have to add and shape some foam to get a comfortable and secure fit.
I believe the Glide seat was secured in place using straps, and could be adjusted forward and back somewhat. It could also be tilted up at the front somewhat by putting foam beneath the front edge and the hull bottom. If so, some seat position and angle adjustment might help get a better fit in the “thigh braces”.
The video shows an adjustable type of foot brace, although the ones in the video are more complex because they also serve to control a rudder. The video also shows approximately how you want to shape the hip pads to fit. I would start on the tight side since you can always remove more minicell. You might think that you won’t be able to exit the boat, but when you are upside down and everything is wet, it becomes much easier than you would imagine.
You can buy 1/4" thick sheets of minicell foam pretty cheaply and cut it with scissors. Glue it in with DAP Weldwood contact cement (the flammable version in the red and black can available at Walmart and nearly everywhere else). You can use this to pad out the underside of the deck and the hull sides where your knees make contact.
keep it simple
practice hip snaps on the side of the pool or with a flotation device
don’t let your paddle dive, make an effort to keep it on or near the surface
bring your head out last
all of it easier said than done.