It's volume licence for Full CRM version I'm afraid, and the minimum is 5 licences. If you are a Partner, then call up Microsoft and see if you can split any existing licences. For instance if you have a company that purchased 8 licences, you can possibly
add another licence on-top of that making 9 (You get your own instance). It's at the full discretion of the rep so you may or may not be able to do this. Failing that you can do what I do and hop from one trial to another.
Microsoft mentioned this at some point before launch when they released licensing options for 2013 that there would be a volume limit imposed, they stated that they would remove the volume limit if there was a large enough demand - I'm assuming everyone
is filthy rich so didn't mind purchasing the 5 licences for one instance.