It's not necessarily meta-gaming. In fact, Richard Sharp describes a St. P to Turkey convoy in "The Game of Diplomacy", calling it a victory lap. I've never seen it done for tactical reasons, but sometimes, if a player is going to win and has a bunch of spare fleets lying around, it's a fun way to show off! :) So yes, it's most certainly planned.
In a game I recently played as France, I allied with Germany. Our alliance worked out, in spite of some initial mistrust and periods of unequal expansion. We reached 16 SCs each, with Turkey having 2 centers left. Germany was in a stronger position, which made it very difficult for me to stab him, and I was a little ill at the time, so I decided to accept a 16-center second place instead of trying to force a win or a draw. I had a bunch of spare fleets, and so we planned to convoy an army from Smyrna to St. P. Unfortunately, we messed up the timing a little, so instead we ended up with a slightly weaker Clyde-Smyrna convoy, though there were fleets in the Barents and Norwegian Seas. The game is at http://phpdiplomacy.net/board.php?gameID=4512, if anyone wants to take a look.
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Draw Request- My First Game -2
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