Two key Labour figures and former Plaid Cymru leader Dafydd Wigley say they would accept a "compromise" plan on more powers for the Welsh assembly.
Dafydd Wigley stepped down as Plaid president four years ago
Environment Minister Carwyn Jones and MP Paul Flynn, who want full law-making powers for the assembly, made their commitment at the National Eisteddfod in Newport.
They said they were ready to accept the solution mooted by Mr Morgan.
It came as Conservatives claimed there would be a high cost of devolution in England.
In March, the commission chaired by Lord Ivor Richard recommended the assembly should be given primary law-making powers by 2011.
It also suggested an extra 20 AMs and a change in the electoral system to the single transferable vote.
But Welsh Labour has already ruled out a straightforward commitment to primary powers.
Mr Morgan has suggested the assembly should be able to amend laws passed at Westminster.
His reaction brought a mixed response from AMs and MPs, with some suggesting he had done a U-turn to appease critics.
Mr Jones, the AM for Bridgend and a member of Mr Morgan's assembly government cabinet, had previously stated that the assembly needed primary law-making powers.
Speaking at the Welsh language discussion forum, Cymdeithas Cledwyn, he said he still maintained his original opinion.
But he said that the model put forward by Mr Morgan would give the assembly the flexibility it currently lacked.
Rhodri Morgan says the assembly could amend Westminster laws
Mr Jones said he believed that a referendum on giving further powers to the assembly could be won.
He said that people in his constituency who voted against the assembly in 1997 were now changing their views on devolution.
He said people "should stop apologising about the existence of the assembly".
Similarly, Newport West MP Mr Flynn said he was still a supporter of a full parliament for Wales, and of the Richard proposals.
But he said those of the same opinion as himself would have to support the compromise if necessary - as the next step forward to full law-making powers.
Mr Flynn also voiced concern about the outcome of any referendum.
Mr Wigley, the former Plaid president, speaking at a meeting of the Parliament for Wales Campaign on the eisteddfod field, said Mr Morgan's proposal could speed up the process of creating a parliament for Wales.
He suggested that "this could be more radical than what Richard proposes".
Mr Wigley said the first minister's idea to amend past legislation retrospectively would need an act of parliament which could be brought in time for the assembly election of 2007, four years before Lord Richard suggested that full law-making powers would be attainable.
The former Plaid leader said a campaign for full law-making powers was still needed, and Mr Morgan's proposal should be welcomed but only as a step towards a parliament.
Mr Wigley stressed that he was speaking as an individual, and was not seeking to influence Plaid Cymru policy.
Meanwhile, the Conservatives claimed that the UK government's proposed regional assemblies for England would cost taxpayers in those
areas £122m a year.
Shadow Minister for the Regions Bernard Jenkin cited the said "the spiralling costs"
of devolution shown by assemblies in Wales, Scotland and London proved that regional government was "fat government".
Mr Jenkin said a regional assembly in north east England would cost £22m a year, £8m in the north west, and £42 in Yorkshire and Humber.
Mr Jenkin said the estimated cost of the Welsh assembly together with the Wales Office had
been £92m, but in 2002-2003 the figure had increased to £177m.
He also said the cost of the new assembly building in Cardiff Bay had risen from £17m to £55m.