A modest proposal
Next election, let's set up a movement to "draft" Colin Powell. Nevermind that he refuses to run. It can be via one party or the other or both or independent.
Then we vote him in. If he refuses to serve, there is plenty of common law precedent for the proposition that an elected official doesn't have a choice. He has been selected by the people, and must serve. Besides, this is C in C of the armed forces. Failure to serve is desertion. If he fails to show for his inauguration, MPs go looking and bring him in and then see him into the White House. He'd probably figure after that that he did command men who had been drafted and didn't want to be privates or pfcs, so he oughta serve as commander in chief even if he didn't want to.
In this I am guided by a friend who knew him, and thought him the wisest fellow he had ever known, and a general that I met at an NRA convention, when I was too intoxicated to remember his name, and a few NRA-linked people who served on his security details. And by the thought that it would be wonderful to be governed by a fellow who had no ego problems, didn't want the big name and celebrity, and had to be forced to attend his own inauguration. He does love to work on cars, but it wouldn't be hard to build a real garage onto the White House, and buy a full set of tools.
UPDATE: I know he endorsed Obama. We all make mistakes. I've made some bad and painful ones. The most we we expect is that a fellow learns from each. If he makes a move and gets hammered, he thinks about where he misjudge events or human nature, and learns from it.