If you have the rulebook, it gets pretty explicit with that tactic on pages 25 and 26 I think. Somewhere thereabouts.
You have to have Advanced Jump Engines on the attacking ship that's in hyperspace and a scout in normal space in order to make it work...
I would say, take 1 WS with Scout and open 4 JPs simultaneously into the center of the Gaim fleet so that scatter will hit at least one of their ships and probably more...