In an article by Stewart Mitchell in PC Pro, and also Cnet (Don Reisinger) it was reported that a recent EU court judgement allows businesses to resell software licensing blocks. The implication is your company can sell software licences which it no longer needs. You can't split the licence blocks into smaller portions, but if you've purchased several blocks for the same software those can be individually resold.
As this ruling was in Germany under EU law you might want to seek legal advice first in other countries before following this route. It will be interesting to see how this affects supplier buyback of licences. No doubt the suppliers will attempt to repackage their licences as services. One company UsedSoft already offers a service in this respect.