Contact a guy named Larry Wiechman.  He does push-button and cable operated compression releases for the 500's.  Had him do my CR500 and now its starts as easily as Cr125.  Seriously I can start the beast in flip flops now!  And the price is only like $100, just send him the head and it comes back looking done right from the factory.  He's well known on the KX and CR500 forums.  Wiechman@charter.net