This is actually very hard to do. You can only do this with missile weapon types (see Phase Missile Barrage on the Vulkoras), and I believe it maybe hard coded to face forward (well you may get it to work, but you will be able to use it regardless of which direction the ship is facing).

If that is not acceptable, your only choice besides the weapon statistics would be to make a very complicated custom particle effect like the Marza's missile barrage.

Edit: Actually I believe phase missile swarm also requires multiple targets, so you maybe unable to make that type of approach target only one target with the broadside.

Look at the Scattershot ability on the Ragnarov (? tec rebels) titan, it allows you to apply buffs to things along a cone on any of the four firing banks... so you'd be limited by the number of instant actions (or you'd have to layer buffs, using periodic actions/delay times, and multiple apply-to-selfs) so...

also there's no "travel" effect, e.g. you'd need to create an effect (to attach to the model via an ability hardpoint which would then play the effect and do damage to everything.  The target cone thing is the hitch- see how wide the scattershot thing is? it's very hit and miss.

then again, if accuracy isn't a big deal (i.e. no guarantee of hitting anything) then you maybe just apply a bunch of these effects, each attached to a weapon hardpoint (though I don't think you can do that with abilities) and a very tight cone.

Long story short, you'd need to do a lot of particle tweaking, to make an effect(s) attached to a single point per side (at least) that would at least passably look like the weapons firing... ask someone with a good bit of particle/modeling skill.