The 'Spartan Laser' would end up being like a SSRL, since it would only be one (highly accurate) shot before you had to dispose of it. Since it would be more powerful than the sniper rifle, I'll have to make it one shot and 3x2 otherwise it would make the rifle useless.
I will investigate the the civilian mod and see if it works
Maybe make the weapon 3x2 with a 2x2 clip that only has one shot? That would represent the high energy power pack being all drained in one shot, but without the whole weapon (electronics, lenses and all) going to waste after one shot. Unless you want to represent the shot being so powerful it melts the weapon, but that doesn't sound very safe to use.
This way, a trooper can still only carry 3 shots (2x hands + backpack), but it's not quite as ridiculous as carrying 3 of the same weapons, and you can have some troopers carrying just a powerpack to toss to the guy with the weapon if needed. Then you can also make the weapon part even more expensive (you only need to manufacture it once), the shot relatively high TUs (so you can shoot once and recharge, but not shoot again) and it is more likely that players won't have plenty of shots when facing sectopods.
Actually, that might be exactly what I'll do for my laser cannon..!