A good call is also to be a fast moving, stealthed champion like Shaco or Evelynn. I'd personally rest on Bot with Evelynn, or jungle with Shaco, and whenever you see an overextended enemy lane, run overthere and shut them down. They're both some of the fastest moving champions you can get your hands on, so I'd look into that.
PS: It is not Top's job to help other lanes untill end game. Top's job is simply to keep the top lane pushed and/or defended so the enemy team dont get an easy push lane. If you truly want to be a lane ambusher, do as offered above, play Katarina, or another hard ambush champ who can mid, and wreck face.
PPS: DO NOT play Ahri <_< She's a horribly gimped champion.