I replaced my stock aero pads on my Felt with Cee Gees (didn't like the stock pads...too slippery with sunblock and sweaty forearms). The thing was, both pads had opposite sides for the velcro. Solution, I bought some industrial strength Velcro strips and cut them to size and replaced what was on the surface of my aerobar armrest to match the back of the Cee Gee's pads (read stories that the velcro adhesive that comes with the Cee Gee's weren't the greatest and would also agree on that along with them not providing enough of it.

Something like this worked out for me and stands up my bike on a hitch bike rack too (my pads are on there very securely) - cut them to the size/shape for your arm rest setup.