The duo will fill the vacancy on a temporary basis caused by the resignation of assistant coach Enoch Nkwe. Duminy was appointed as head of batting department for the Lions in the 2021/22 season. Sammons, who has previously worked with the Lions, is the coach of North West province.
He is currently in Sri Lanka with the white-ball team as a batting consultant.
"Justin previously worked with the Proteas during the first part of our current tour of Sri Lanka so he has already developed a good working relationship with the players. JP is a perfect fit for T20 cricket. His record as a player speaks for itself and he will bring specific skills in all three disciplines of batting, bowling and fielding," said Graeme Smith, the director of cricket at CSA.
"I would like to thank the Imperial Lions and the North West Dragons for making JP and Justin available to us where they are currently employed as the respective batting coaches," added Smith.
South Africa named their 15-man squad for the mega event on Thursday with notable absentees in the form of Chris Morris, Faf du Plessis and Imran Tahir. They will open their campaign in the T20 World Cup against Australia on October 23 in Abu Dhabi.