I don't think FT should endorse people playing dumb. We expect honesty and integrity from the airline. I think we should expect the same of ourselves (as a community).
If the OP wants to play dumb, it should not come with our blessing!
If it were me, I would go to the airport and explain the truth. You want to get home early (to be with family, to watch the football games, to play tiddly-winks, whatever!) I think the agent can usually see through playing dumb.