Seems like a bit of awkwardness and inflexibility on ebuyer's part... Unless someone comes up with a better solution I'd be tempted to post in ebuyer's own forum - a lot of their staff are active on there and I've seem many issues resolved by simply being read by the right person that is prepared to put in that extra bit of effort for a particular issue.
An example that springs to mind was someone that had bought a case + PSU combo where the PSU turned out to be faulty. They phoned ebuyer and were told they had to return both PSU and case as it was sold as a single item, even though the customer had already built their PC. The customer then posted about it on the forum where someone higher up read it and realised it was both a waste of time and money for both parties, so told the customer call back and tell whoever they spoke to that 'Kirby' had authorised the customer to return the PSU only.