My answer would be that you shouldn't, and I must say both as the one who asks, as well as the author of the accepted answer, I'd consider it a kind of a contempt.
while anyone has the right to vote for (or against) the quality of an answer, it is the exclusive privilege of the one who asks to accept whichever answer he or she considers most useful. OP does not need to defend his choice, nor should anyone use any pressure to accept this or that. I have seen it in the past more than once, and found it horrible without exception, Not to mention that I often disagreed with the claimed "this is the best answer".
Really good answers will often attract more votes over time, accepted or not. The gloomy attempt to push someone simply isn't serving any goal.
