Bellamy scored Cardiff's second, while Helguson provided late assists for Lee Mason and Kim Bo-Kyung as the Bluebirds made it five wins in six unbeaten games.
Mackay said: "You can't treat everyone exactly the same in terms of how we train them.
"The 19 and 20-year-olds are trained slightly differently to the 34 and 35-year-olds - I wish it had been like that in my time but it wasn't.
"Craig and Heidar will have a day during the week where they'll go to the pool and do some stretching and not go out on the grass but come 7.45pm on a midweek night and 3pm on a Saturday they show that experience.
"Craig's been out for four weeks this season with a swollen ankle and a couple of weeks with a knock to his knee but I want bravery.
"He shows it every day in training. He wants to train every day and I have to pull him back and say 'no, you're going to the pool today'.
"The work that him and Heidar did for the second goal was incredible - he flicks it on to Heidar, Heidar flicks it back to him and he puts a magnificent finish in.
"They've both got their heart on their sleeves and that's what I like."