I have seen this tip on this board and it has helped me greatly.... It works and you don't lose your reservation.
Using two devices or two browsers, Start booking the new reservation on your computer. Get to the point where it says the reservation is held for 20 minutes. There will be an option to borrow points on this screen. Now, on another computer or browser cancel the current reservation. DON'T DO ANYTHING ELSE. Don't search for availability or anything else on the the other computer just cancel the reservation. Go back to the 1st computer and select the "Borrow points" option. Then click cancel. Your point totals will refresh without losing the "hold" on the new reservation.