From the FAQ I saw this, which suggests that you can purchase as many sets as you want - probably have to make multiple registrations though, but could mean a member going (like me) can buy the discounted sets for other people here, plus a loose set each time as well. (would have to still post them back though)
It's probably how the dealers get their hands on so many sets each year.

Question: Are we allowed to buy more than one primus package per membership or is there a limit of one per?
Answer:Yes you can purchase more than one as well as purchase one loose set per boxed set you bought. You only get one name badge at the convention even if you have multiple sets.
I can't afford to buy extra sets on my own, but if purchasing extra sets is possible, I might be able to do this for others who send me the money beforehand. Especially if it looks like they might sell out in that first week before non-attendees can order.
(not sure if the attendee figure is given one-per-person or one-per-set if ordering extras)