Defence coach Kevin Sinfield revealed Harlequins star Smith has jumped at the chance to try the new position, enjoying cameos against Ireland and Fiji last month.
Fly-half Smith had never played in the No 15 role before, but insisted he would relish the opportunity when quizzed on the challenge by Sinfield.
The 24-year-old could either cover both 10 and 15 from the bench against the Pumas in Marseille – or edge ahead of Freddie Steward in England’s starting XV.
Leicester star Steward has been an ever-present in both the tail-end of Eddie Jones’ reign and Borthwick’s full nine-match stint as head coach.
Smith would offer a livewire attacking dimension from the backfield though, leaving Sinfield excited about the extra options his game-breaking talents would provide in the position.
“It was a question I posed to him, ‘have you ever played 15?’,” said Sinfield. “His first answer was, ‘no, but I would love to’.
“He embraced it straight away. That response was music to our ears because you’re looking for tactical variation in the players we select.
“And when you’re putting the team together the 15 and then the bench, understanding who can move where.
“We started utilising some of this in training long before Anthony Watson sadly had to pull out, who possibly could have been an option at fullback as well. It gives us a bit more variation.
“So, the initial answer was wonderful from him. But we’ve worked on it in training, we’ve seen him play there. If through running somebody there in training there were any doubts, we wouldn’t have continued with it.”
Sinfield hailed Smith’s creative genius as offering England an almost preternatural extra edge with the ball in hand.
“You’ll have all seen what a magician he is with the ball, step off both feet, quick, can beat the opposition for fun,” Sinfield said.
“So why not try to give him a bit more time and space than he would typically get at 10, try to get him a little bit wider? We have been working on it for some weeks now with him in training.
“He’s been incredible at the back. To have him in the team and available, to have the option of him either coming on at 10 or 15, has been really good for us.
“His combination with George Ford, as well, and with Owen Farrell when he’s been alongside him at 10 and 12 not 10 and 15 just gives us a different way of playing.”