You cannot make a cash reservation to "hold your place in line". If you make a cash reservation and then want to switch that to a points reservation, you have to cancel the cash reservation and then book a new reservation using points. But you can only do this if there is availability. If the resort is booked up, you can't just convert the cash reservation to a points reservation in your name.
Also, I'm curious about your phrase "when points become available." The only controls for when you can make a points reservation are the 7 and 11 month windows. You only have to worry about use years and points being available when looking at the time of your trip - not the time of your reservation. Hope this makes sense.