Hi Jon,
theres a couple of things you can do...
a) make sure you moisturise your ball sack, it helps keep the skin soft and eleastic
b) when you get out of the shower or bath and while youre in it, pull and stretch and tug on your balls
c) every day, whenever you can, use your fngers and thumb and wrap them around your balls in a cup shape and pull down on your sack, youll be surprised how much it will loosen and stretch.
Do that for a while and youll be fine, let me know how you get on but take it slowly, dont rush ok?
ross