Long Service Leave

WE have both Full time and Casual employees. I have loaded the LSL entitlements for the full time employees and set the accrual to weekly no problem at all.

My problem is with the casuals - All LSL is calculated in weeks not hours however MYOB Payroll only gives an hourly option - the casual payment calculation for LSL is based on the average hours worked over a 1 or 5 years  (which ever is the highest) so when we pay a weeks LSL it may only be for by way of example 16 hrs. Each casual would be different with some working 2 days others 4 to 5 

My question is - do I enter the entitlement as 8.667 weeks converted to the hours worked on average by the casuals - this option would never be totally correct as the actual entitlement is calculated for the 1/5 years preceding the payment 

Am I overthinking this ?