Sure. We sell them here: https://pakayak.com/shop/knee-and-thigh-pads/
The braces are attached using velcro. You place one part of the velcro on the inside of the kayak (the soft side) for your hips and the other part on the back of the hip pad (the more abrasive side). Repeat on the other side.
For the knee braces, place one part of the velcro on the cockpit pad about half way up, and the other part on the back of the knee pad. Repeat on the other side. 
The velcro allows you to remove them to nest the kayak. The velcro is quite durable, sticks well and is waterproof.