Scott Morrison, John Howard swing in behind Jim Molan's return to Canberra

The retired army major general's bid to fill a casual vacancy created by the resignation of Arthur Sinodinos has also won the backing of John Howard and Sydney-based broadcaster Alan Jones.

Prime Minister Scott Morrison has committed his "strong support" to Jim Molan's return to the Senate.

In an email to delegates ahead of the vote on November 10, Mr Molan has circulated written references from the trio to let them know how he "might best help the Morrison government beat Labor [and] the Greens".

The party remains fractured over the potential for his return, with many still angry about his rogue campaign to convince people to disregard the Coalition's Senate ticket and vote for him "below the line" in the lead-up to the May 18 poll.

Mr Morrison heaped praised on Mr Molan's "energetic and spirited efforts" in the seat of Eden-Monaro during the election campaign, which he said was reflected in the esteem he was held by community groups and local residents.

Mr Molan missed out on a Senate seat, despite attracting more than 137,000 below the line votes.

"Jim has the leadership and life experience to continue to contribute to public and political life in New South Wales and Australia from within the Senate," Mr Morrison wrote.

The NSW conservative faction's leadership body - known as RELM - agreed to support Mr Molan's candidacy at a meeting earlier this month.

He will be challenged for the spot by former federal MP Peter Hendy, who is pitching himself as a non-aligned "compromise candidate", Woollahra council deputy mayor and former party state director Richard Shields, and Sydney surgeon Michael Feneley, the director of cardiology at St Vincent's Hospital.

Mr Hendy has support from Sir Angus Houston, the retired Air Chief Marshal and former Chief of the Defence Force, as well former NSW premier John Fahey and his former employer, ex-foreign affairs minister Alexander Downer.

Frontbencher Alex Hawke - a close factional ally of Mr Morrison - has pledged support for Mr Molan, describing him as "ready to go".

Mr Morrison said in his reference Mr Molan had "worked hard, both inside and beyond the Parliament" and was "held in high regard by his Coalition colleagues".

Mr Howard wrote that Mr Molan "gave so much" in his "all too brief service" to the Senate from late 2017 to June 30 this year and was "crucial to the success" of the Abbott government in his advisory role to Operation Sovereign Borders.

He said his return would strengthen the Liberal team in Canberra.

"There is nothing grey or bland about Jim Molan," Mr Howard wrote.