Get to the lounge early, load 20 cans of Heineken beer into your carry-on (ignore the FTers giving you the Stares) and get to your seat. Shoes off, "little wings" on the headrest out, and then 1 can per 10 mins for the first hour and 1 can per 15 mins after that. When you wake up with "ten minutes till landing" the helpful BA crew will have taken away the empties and you will be good to go!
Seriously..... dont expect to sleep and a be grateful for the couple of hours dozing if it happens. A good book or documentary series on your ipad will help.
My best recommendation is to read the WIKI forums on how to gain status and TP runs. I did it about 6 years ago and have had a lie flat bed ever since. Thanks FT community.