Requesting for permission to work overtime or on holidays is a task that is often neglected. Sometimes people end up reporting it after it happens, or forget to report it altogether unless sent a reminder. This makes it unnecessarily hard to calculate salary payments at the end of the month.
You may want to find an incentive that makes people submit overtime requests in time, but if that's not possible, at least to make them report overtime hours without being told. You could have the boss get mad, have Accounting send a complaint, or have someone else submit the reports... but none of these seem practical.
The important thing is to make sure people are aware. And for this it is convenient to automate things. If you have a time-card system that logs the time each employee enters/leaves the building, you could connect this to the workflow system so that a "request for permission to work overtime" task is automatically generated and put into his/her task list. (Start process by HTTP protocol)