If we could have beams curving away from a target, or decohering near one, we would have done that. Unfortunately, the engine doesn't know how to do that.
Well...you might be able to achieve an effect that's similar enough but still possible with the FSO engine. I'm just taking a stab in the dark here, but something along the lines of a beam, primary cannon shot, or even secondary weapon that's modified/designed to look something like an incoherent stream of plasma might do the trick. Create the beam/shot/projectile, then FRED the turret(s) in question to manually fire it at the right time and place.
I've actually made something (very) vaguely similar in concept as a weapon I've been trying to flesh out. Though the specifics would need some major changes, the basic concepts involved might be enough to create a makeshift solution.
I'm thinking...if going with the primary cannon shot route...a laser shot with a crazy rate of fire (looks like a stream, or close to it if you'd like that), very different head and tail widths, long laser length, unstable-looking color patterns in the start and end colors, changes in the alpha levels as necessary, and huge width in general (to look like a beam cannon that is incoherent, with a loose and warped magnetic bottle). If there's a way to randomize those exact numbers as the beam/shot fires continually, it might get the kind of effect that you're looking for (even if an Aristeia-like shot misses its target completely, it would still have the effect of an incoherent, disrupted beam).
Or, maybe, a missile route--the missile looks like a beam (like the Shivan Super Laser), the trail is super-long, and the missile's tabled trajectory/flight pattern is curved in a designated way (corkscrew, extremely poor tracking combined with an invisible countermeasure via FRED slight-of-hand, maybe?) for the desired effect?
