This sounds very fiddly and extremely inefficient.
Gravity guns cannot "intercept" projectiles in the sense that you're thinking at least from an engine perspective. You could write a hack for this, but it would not be pretty. Essentially when a projectile is marked as intercepted in spring, it will be deleted. You do not want this for your funny impulse to projectiles gun. You would need to run the following calculations in one intercept loop:
1.) Whether or not the projectile will hit (and splash) anything allied. (important otherwise it will be janky and players will get frustrated)
2.) The projectile's "mass" -- you'll need to implement a custom calculation to make this work.
3.) The angle at which you're pushing the projectile.
4.) How much strength you're inflicting onto the projectile.
5.) The new fixed velocity using the angle in step 3 with the velocity impact of step 4 and applying it to the projectile.
Then finally draw a fake "gravity laser".
Complication: ZK grav guns are not beam lasers and there's no AllowProjectileInterception. There's allowing a unit to target a projectile during a perodic sweep, but nothing else. You'd need an engine FR for this to work, most likely.