An odd idea...

[Siven]

Due to the length of Soul Voice, compared to other 30-sec abilities, if you log out immediately after you activate it, and come back two hours later, you'll still have about 90 secs of it left (assuming 2 mins duration, which I'm too lazy to verify), plus the chance to use it again. So theoratically you can have perhaps 3 mins of Soul Voice for a difficult battle. This probably takes too much coordination to pull off usefully, but just a thought.