I often stealth cap, and most of the time I can do it without having to stun/mez or attack an enemy player. Very often win game after game (of hypergate especially), due to poor defensive placement. Defenders standing infront of the node or on it are a prime example. I can be stood right behind an opposing player capping and he doesn't even know. Even better is if they run to centre with 10 secs left to cap, which also happens frequently.
Getting one other player to attack the pylon from range will always pull away silly defenders, which is great if you are placed to cap as soon as the enemy make a move. It is making sure that your team mate does nothing to draw attention to your position. so staying as far away as possible, and not moving in a direction that will change the enemy players los.
Timing and communication is everything. I alway attack hypergate pylons with 10ish seconds left, and in other games as soon as possible while most of the enemy players are attacking the heavily contested node. If it's a battle I can't win I either suggest we could take it easily with one more or go help elsewhere.
The minute or so at the beginning of every warzone i will always say what i am going to attempt. Even when you don't know the players, using this minute before the game starts to establish a little bit of communication can bring the rest of the team out of it's shell. Stealth capping will always be just one of many tactics just like attacking East and West, and leaving centre in Novare Coast thus throwing off the opposing players.