Instead of launching an invasion to overthrow the government of Saddam Hussein in 2003, have the United States and Britain find a way to resolve disputes over weapons of mass destruction either through negotiation or limited military intervention not significant enough for a full scale war.
I have never seen any convincing evidence that the WMD dispute had any actual basis in fact, as opposed to being a completely made-up pretext by the US and Britain created to justify the invasion. This means that there would have been no actual dispute to be resolved diplomatically, since there were no WMDs to discuss about anymore*, and the American administration very likely already knew that (though Bush may have personally believed the lies his staff was propagating).
Since the actual aim was, almost certainly from the start, to topple Saddam and install a pliable Iraqi government in his place (and/or dismembering Iraq, a policy that was publicly considered and may even have been more sensible - for a given value of "sensible") nothing short of Saddam stepping down and peacefully letting the West occupy his country for a while is likely to work.
* Of course, Iraq DID have chemical weapons in the eighties, and liberally used them. Republican US administrations back then do not go on my record as having been very concerned about that.