You borrow points when you make a reservation that needs them. You will not be able to borrow Aug 2013 points for a June 2012 reservation. This reservation will be in your 2011 UY, thus only being able to borrow your 2012 UY points.
I don't know how many points you need, but don't forget you have the option to buy one-time points from Disney to complete your reservation. You can't do that until 7-months out though. Still, it may be a possibility for you. You could also do a cash reservation for one or more nights to lower the points needed.