Is this a business first trans-Atlantic award?
Your best bet for having the seat clear is to be a platinum member. Depending on the day of the week and of the month, the likelihood of the upgrade clearing is slim to none on such an elite-heavy route where business travelers will often purchase the first class seats.
If you see mileage availability open up on the seat, call them and ask them to confirm you into it (although its supposed to be automatic, Ive seen otherwise). Alternately, if there is another flight with open seats in First that will get you where you want to go, ask them to confirm you on that flight.
Safe travels!