Airwave, I had that idea 20 years ago when I used to travel from NQY-LHR. Trying to get an up-grade by bribeing the check-in staff with Cornish goodies such as Saffron Cake and fresh Clotted Cream, claiming that "some-one from the London Office was supposed to meet me with some documents but they haven't turned up". It never worked. So after a couple of years I gave up, only to be asked once, where the goodies were!!!
You cannot win. A full flight, a winning smile and patience is by far the best way to get upgraded.
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Wake me up when we get there