In OZ we get 1.85 hours pay for each hours OT. With the minimum payment for OT on a day off of 4 hours pay at 1.85.
We can exchange OT for TOIL too, but you get 1.00 TOIL credits for 1.00 hours worked; so most people take the cash. When we accrue TOIL allegedly we can't hold a balance in excess of 2 days; although this isn't strictly policed. Some TOIL isn't officially recorded and has caused problems when individuals try to claim it back.
Seems to me if your swings and roundabouts system is all swings then you need to get a payment system fast or an ability to say NO to extra shifts if you haven't got that ability.
A good solution to your problem is to recruit more staff; there are plenty of Aussies willing to jump on a the slow boat to honkers without too much pushing at all I'd bet
