We were at WDW for Marathon weekend this year, and we were able to move our reservations from VWL to BLT. We had to waitlist, but a 2 bedroom dedicated lake view came through at 6 months. Maybe it was because of new inventory, I don't know, but still, we got it in plenty of time.
I'm guessing that you have until the 7 month mark to book. My DDiL had tore her ACL and didn't run as planned. DH, and DSis did the family run and we had a great time, but it was very very cold!
Best wishes to you as you train! DH is considering trying the 1/2 in 2012!
Bobbi