His two wickets in his first over against England in Hamilton last night provided just the tonic for the hosts to go on and wrap up a convincing 55-run victory to square the series ahead of the decider in Wellington on Friday night.
''We look to try and use him in an attacking option throughout," McCullum said.
''That's his brief, to run and try and take four for 20 every time he's at the wicket.
''Sometimes it's not going to work; you could easily go none for 50.
''But we're trying to instill confidence, to be aggressive and most of the time he's delivered for us. He's really progressed as a cricketer in a short space of time."
In three ODIs in South Africa, McClenaghan took six wickets at 23.5; in five 20s, he's taken seven wickets at 18.4.
His sights are now set on establishing himself in the ODI side - that three-game series against England starts in Hamilton next Sunday - with half an eye on the 2015 World Cup, to be hosted by Australia and New Zealand.
''That's my goal, to get in the team and cement myself with the World Cup coming up. I really want to be established with 20 to 30 games in the team by then."
But for now, there's business to attend to in Wellington on Friday night.
''We really need to make sure we keep on winning. That's how we get our support and repay the faith," he said.