The club are without seven first-choice players due to injury and international call-ups, prompting a move for batsman Mark Stoneman.
Joe Root, Jonny Bairstow, Adil Rashid, David Willey and David Malan are with England, while Tom Kohler-Cadmore (broken finger) and Will Fraine (side strain) are out for around three weeks.
Stoneman, the Surrey left-hander who is not part of their first-choice T20 team, debuted against Northants at Headingley on Saturday, scoring 50 as Yorkshire Vikings won by 82 runs.
“With the number of players we are now missing due to England commitments and injury, we felt we needed to add a top-order batsman to our squad for the latter stages of the group,” said first-team coach Andrew Gale
“We have made a great start to this year’s Vitality Blast and seen some great contributions from some of our younger players, but feel like the addition of an experienced batsman at the top of the order is important to help keep up the momentum. Mark Stoneman clearly fits the bill for what we are looking for.”
Stoneman, who turned 34 on Saturday, was brought in to open the batting with Adam Lyth.
The former Durham man, who played 11 Tests in 2017/2018, is available for the remaining group games apart from Notts at Trent Bridge on July 9 as Surrey want him back to prepare for a Championship fixture.
“I really enjoyed it,” said Stoneman. “It all came around pretty quickly from getting a phone call at 1pm yesterday on the way to training with Surrey.
“I’m really grateful for the opportunity, and it was nice to get a score on the board and a couple of decent partnerships with the lads. I’ve been welcomed with open arms. It’s a great opportunity for me, and the club saw the chance to bring me in and use my experience and skillset. It’s the perfect balance really.”