Last couple of years I've just emailed
ticket@lemans.org stating 1st & 2nd (and even 3rd) preferences for camping & grandstand, and supplied a full postal address. I had asked the agent who was dealing with this year's ticket dispatch if she could confirm they were opening booking requests on 3rd June (which they told me earlier in the year) and she said (on the 2nd) that "you can send your booking today, it's opened"...
Now there's the fingers-crossed 6 month wait to make sure they actually *got* the email, and have put it in the appropriate place in the queue...
Ewan