The Reds will line up for the sudden-death clash on Friday night after also taking on the Crusaders in the final round of the regular season.
On that occasion, they couldn't match the home team in the opening stanza, trailing 21-3 at half-time. While they rallied for a 28-15 scoreline, the game was effectively over early.
With co-captain Liam Wright returning from injury to replace McReight, who has been one of the Reds' best, Thorn is gambling they will be in the fight at halftime before the livewire flanker makes his entry from the bench.
But he will consider early changes if required as the Reds look to end a horror 0-5 run for against Kiwi teams.
They have been given little chance, with bookmakers quoting $12.50 for a Queensland win.
Remaining in Christchurch through the week, Thorn said Wright gave them more grunt at the set-piece.
"We'll be ready to adapt to any situation," Thorn said on Thursday from Christchurch.
"Liam Wright coming in is our co-captain, supporting Tate (McDermott), and just around our set piece and lineout with his knowledge and experience there.
"The Crusaders started well and we were trying to fight back from that and I was really pleased that our finishers came on and brought energy and Fraser is going to be a really important part of that.
"Back in the 1980s or 90s you only got on with an injury but squads of 23 are so important - they often come on when it's crunch time.
"Every team wants to start well, it's important, but we think those guys on the bench can bring real energy."
Hit-man Paisami has been sidelined for a month with a shoulder injury and Thorn said it "makes sense" not to try to get 80 minutes out of the Wallabies centre.
The Crusaders have been bolstered by the return of All Blacks trio Jack Goodhue, Richie Mo'unga and Codie Taylor.
Former Argentina skipper Pablo Matera is in the Crusaders starting side after he escaped further sanction from SANZAAR despite dumping Reds centre Jordan Petaia on his head during a clean-out last Friday.
Thorn said he had contacted officials about the inconsistency in their decision given Highlanders five eighth Sam Gilbert was banned for five weeks for a similar tackle of Waratahs flanker Michael Hooper.
He said though that the Reds needed to put it behind them.
"I don't really understand it," Thorn said of the lack of penalty beyond a yellow card.
"We have had time with officials ... going on the NSW game with the Highlanders the week before, the outcome there, just the consistency, and also the safety of players.
"It was positive feedback but it's gone now and it's all about Friday."
