What if the UN handled post-war Iraq?

I've been participating in a comments thread over at Belgravia Dispatch lately. I've tried repeatedly and unsuccessfully to get Greg Djerejian, whose opinion I value enormously, to comment on the impact UN participation might have had on in post-war Iraq. I think my final comment was important so I'll re-state it here (with minor edits).

Sean: "The reality is that, as erg notes, the vast majority of world opposed the war in Iraq, and they did so for perfectly sound reasons- the United States failed to make a case for war."

While that is definitely true, I keep wanting to stress the role of international collaboration in raising the competence of post-war nation building. Like many I predicted the lack of credibility that would result from not having UN Security Council backing for the Iraq war, but I did not anticipate the gross incompetence. Looking back, however, it makes perfect sense: If an administration is left to do invasions "as it sees fit" it has no reason to listen to anybody, be it Democrats, the State Department, UN nation-building experts or heads of European states.

Many people are starting to realize this. I already pointed out what Fukuyama said:

The one area that I've rethought concerns international institutions. I believe that the conservative critique of the legitimacy and effectiveness of the UN is right, but that we need a world populated by a multiplicity of others kinds of organizations. Iraq has changed my view on this.

(Of course he's been a proud "conservative" UN basher for years so he has to put in a disclaimer about the "legitimacy and effectiveness" of the UN, but I we get the picture.)

And departing Economist editor Bill Emmott in his farewell editorial hints at the same thing:

The only argument against our decision that seems to me to have force is that a paper whose scepticism about government drips from every issue should have been sceptical about Mr Bush's government and its ability to do things properly in Iraq.

He doesn't say explicitly that being forced to run decisions by allies through some sort of UN cooperative mechanism would have made for better decisions on issues like army disbandonment, prisoner treatment and the importance of law and order, but in that seems like a logical conclusion.

Governments tend to benefit from a bit of checks and balances. It seems reasonable to assume that Republican idealists engaged in nation-building might as well.