One other option you have is to book dummy return flights that are within your booking window. Date and time changes are allowed and free, so you could change the return to the dates you want (assuming availability) when they become available for booking. A drawback to this process is that routing changes are not allowed, so you are locked into the routing you pick for the dummy return flights and must hope award availability opens up for that routing for the dates you actually want.

I booked a 3 week OW award trip to Australia for 2 in J last August for travel this July. Because I wanted to preserve my flexibility, I waited to book until my return flights were within the 5 day hold window. I was able to find availability on almost every flight I wanted, given that I had flexibility. Waiting to make the booking only cost me one flight that I really wanted, but I was able to substitute another, only somewhat less desirable flight, when the time for booking arrived.