adding buttons to non deviation Devo F7?

Is it possible to add button(s) to the Devo F7 Tx?

also, what is the possibility to add one of those Playstation joystick replacement to one of the controllers that have the ability to add buttons to (like the Devo 7E) this would be awsome to control the gimbel with a joystick

this is what I'm talking about
www.ebay.com/itm/Replacement-Parts-Thumb...2:g:mp0AAOSwjVVVoF74