Perseverance is the key if you want to secure an upgrade beforehand. I wanted to upgrade two of us from J to F. The first time I called the Platinum line they said no reward inventory had been released, called again a few weeks later and was told they'd been taken. I kept calling, probably every week or so, for several weeks. About 4 weeks before the flight I managed to get the upgrade, so additional reward seats must have been made available. On the return we asked in DOH however was told no upgrades were available.
I've given up for my next trip and am just going to ask at the airport.