Okay, our GM and I have been chatting for a bit and have come up with a house rule. When using the Multiple Attacks rule with a gun firing multiple bullets, you split your dice pool as normal. If your targets are within (number of bullets in burst/3) meters of each other they all take the full burst penalty, otherwise you must split the bullets between targets (for instance, firing Full Auto (simple) at two targets 15 meters apart would mean that either both targets are getting 3 bullets [-2 dodge], 1 target is getting 2 and the other 4 [-1 and -3 dodge] or else 1 and 5 [no penalty and -4 dodge]. However, if the targets were merely 2 meters apart and the area was sprayed with bullets both would receive the full -5 penalty of a full auto (simple) attack).
The logic should be fairly obvious, but are we overthinking things?