Well if we take emjaycee as correct (and I'm inclined to agree with him here):
For cap purposes (not contract law purposes) it may suffice to report to the NRL at the end of the year "we paid an extra $400k to Player X this season above our initial estimate" and then next season estimate "$400k less than his registered contract amount for that year." Now obviously the NRL could reject this, but reading into Gould's comments it sounds like they are ok with that arrangement (probably dollar figures depending), although evidently with NRL management it would also depend on wording of contracts, clubs/players involved, time of day, bee migration patterns and a dartboard for them to decide
Edit - note
@emjaycee I'm not putting words in your mouth, just agreeing with your general explanation on salary cap reporting procedure. I may be putting words in Gus' mouth, but that's better than what
@hindy111 wants to put in there