Trouble then is, who buys it and how?
Well I would reckon the Iraqi move was aimed at mainly EU countries and basically all countries other than the US. Of course,
it made little sense at the time because Iraqi oil revenue was held by the UN in an escrow account in New York. But perhaps Saddam wanted to poke the US in the eye and look forward to a future
after sanctions when he would have access to the oil revenue again and Iraq could decide where and how to bank the money.
Using a mish-mash of figures from after 2003 and supposing they roughly applied to 2003, then in 2016, oil constituted over 99% (but not exactly 100%) of Iraqi exports.
In 2015 the main export partners were:
China 22.8%
India 20.4%
South Korea 11.3%
United States 7.8%
Italy 6.7%
Greece 6.1%
Netherlands 3.5%
Taiwan 2.6%
Spain 2.4%
Singapore 1.9%
Japan 1.9%
France 1.8%
Poland 1.3%
Germany 0.9%
Brazil: 0.9%
Assuming these percentages also held for 2003, then in 2003 the countries using the euro accounted for 21.4% of Iraqi exports. A further 1.3% would have been to Poland which was in the process of joining the EU and traded extensively with the euro members and would thereby likely have some euros to pay for Iraqi oil. Brazil accounted for 0.9% but Brazil has historically traded more with Europe than the US if I remember correctly (so there would be an incentive for Brazil to accept euros for payment of some of its exports to pay for Iraqi oil imports). All in all, about a quarter of Iraqi oil exports were to countries that either used the euro or traded heavily with countries that did and this doesn't take into account China, India, Singapore, Korea and Taiwan (although China's yuan was then fixed to the US dollar and wouldn't be officially de-pegged until 2005, but Saddam had likely little way of knowing that).
As to how it would be done, I suppose Saddam could have come up with something like (or later looked at)
Iran's efforts to do the same in 2007.
In fact had it continued and most sanctions been lifted by the UN (even if retained by the US) Iraq and Iran might have cooperated on euro payment for oil after 2007.