The problem with that is that a 5GB bolt on bundle can be cancelled at anytime, so there is no way for Vodacom to ensure that the contract runs for it's full term, which means that they may want penalties to be paid to cancel it.
Thinking out the box is good, but often in a large organisation the solution you come up with cannot be implemented because of the constraints of the systems in place. It's simply not cost effective to re-write a system to suit one customer, even if they spend more than average (but not that much compared to their corporate clients).
I spoke to one of the guys, and what Syndyre said is possible(by theory).
The downside is that the Data Contract will have to canceled, meaning the penalties will have to paid. There is no way to merge the 2 contracts.
I understand that but they could still hold him contractually liable for the 5GB, it'd just be accessed in a different format. That's often the problem with organisations, they become large and then inflexible and start to stagnate. I wouldn't advocate that as a good thing and I don't think its inevitable.