Washing down the arm (drawing Uke in) and the Wrist are the Keys to good Kotegashi.
It's kind of a grainy vid but here is Nishio Shihan's intergrated view in one of his last Seminars.
Done correctly Uke's own weight gathers at his wrist and the technique "happens" naturally without much too effort.
http://www.youtube.com/watch?v=NFodznUgiAU
William Hazen