The obvious solution is to roster the overtime the same way as other shifts. The EBA stipulates that reasonable overtime should be completed, I don't see why controllers should not do 1-2 additional shifts every 2-3 weeks. This is normal in other companies and it only seems to be the controllers that have a problem with it. ASA has a robust fatigue management system and therefor the constant complaining about fatigue is absolute rubbish.
The airlines and customers should not have to face delays just because the controllers don't want to play their part in the system. We need a clean out and those who don't want to support the company should just go.