If you want to be able to use borrowed points for the Oct 2012 reservation, you can't have any 2012 points available when you go to do it.
Also, you can't book the August trip with 2012 points that are tied up in a reservation so if they are currently being used for the October reservation, they can not be used to book August without canceling that.
As suggested, what I would do is book a 2nd October trip using borrowed points first, then cancel and book August.
I will say that I had to do something similar last week--I had to cancel a SV studio at BLT so I could end up booking it with borrowed points--I wanted the current UY points associated with it to go for a Dec reservation.
Anyway, they didn't have SV available but only LV--I figured I would be losing it but did it anyway.
In the 10 minutes between cancelling the BLT SV studio, booking the Dec trip, and then re-booking that studio, the computer didn't claim my SV studio and I got it back.
So, there was either no one on a wait list or, it takes the computer longer than 10 minutes to snatch up a room for a wait list match.
Good luck!