It would have been easier a year ago... but here is my idea.
(1) We have to have enough troops to create secure elections, 200 to 300 thousand troops. (!)
(2) If you can't control a city... people in that city don't take part in a democratic process unless they go to a controlled area. (wouldn't have needed this so much a year ago)
(3) You need several thousand election monitors and officials.
(4) We begin polling on governmental preferences in every villiage, say within 5-10 miles of all population. This goes on for three months.
(5) A constitutional section is written (by whom? you may ask) which is the Constitutional Requirement, it involves a guarantee of elections at least every 4 years and a bill of rights to ensure the rights of individuals. It is imposed on the process.
(6) You continue to poll the Iraqi people, processing the results, at the least by publishing them.
(7) You use the polling aparatus, with kinks now worked out, in order to elect local delegates for regional constitutional conventions.
(8) Regional constitutional conventions are held. International and Local elections official regulate not only the convention, but clarify the constitutional requirements. These conventions create constitutional proposals of one paragraph to one page.
(9) Regional elections are held to elect national constitutional conventioneers.
(10) The national constitutional convention is held, during which the document is written. An international/local panel will judge if constitutional requirements are satisfied.
(11) Democracy
You require election monitoring for a time of 50 years. Sad fact but I think someone has to leave international/US bases there for that duration to ensure that, if not, we have to be ready to invade... so better to leave them and have a regulated Iraqi military for at least that time period.