Or have him point out a target causing all nearby archers to increase accuracy.
Okay, this is the model I'm completely against for Heroes. It's fine if you want a spell caster with Air magic to do some hocus-pocus to increase range, but not for these Heroes - it needs to be plausible. The archer's range at the present is governed by the physical limitations of the bow, not his limited determination and vigour. Hence why would a hero increase range *and* accuracy like that, just by pointing?