okay, my number one choice is always the master ball.
but if that doesn't suit you, then here:
Send out a pokemon with incredible health, and is a staller @ lv. 65 atleast. (i used Venasaur, but Ludicolo and Exeggutor work too). Next, put it to sleep, then sap its energy, and rinse and repeat until he gets to between 5-1 hp, then just keep hucking up timer balls, and you should eventually capture him, however i would suggest you save before hand and reset if you mess up.