I'm no help personally- DS was 26 months and wanted to go to the "big kid class" at preschool because they had a computer. He trained himself in two days. However- I did watch my good friend train her VERY stubborn 4 year old. Yes... 4 year old.

She told him "Today you will go on the potty, no more excuses." Then she did kind of a reverse time-out. When he was in the bathroom, she read stories, played games and talked to him. When out, she completely ignored him and left in in the living room with nothing to do. She set the timer for every 20 min to go in the bathroom and went in there on her own to play etc. It worked like a charm because that was where the excitement and attention was. It took one full day of this and everything was fine after!

Now, he was much older and very obviously ready. But if you have an older stubborn one, it might work for you!