I've been looking into doing something along the lines of a shotgun spell myself (though more with elemental projectiles rather than arrows), however on looking into it, Skyrim doesn't seem to use spread - be it for spells, bows or projectiles, the only thing even close to that is the cone spread used for cone-shaped projectiles like shouts, which I imagine would be difficult to implement as a multiple-projectile setup and at best would mean no randomness in the flight paths of the projectiles if using separate projectiles as impact points using that was even possible (which again I doubt is the case). There might be a way to do it that I have missed, but at the very least it's beyond me.
