[DF] Stealthy Archery in Forests

[VariousRen]

I'm running a dungeon fantasy game with a strong focus on wilderness adventures and travel. Two of the delvers are particularly well suited to ranged combat in forests, with stealth scores of 19 or 20 and camouflage scores of 14 or 15. DF2 has solid rules for roguish types backstabbing in melee combat, but those rules don't seem to provide much support for distant bow attacks that might not have you instantly spotted. A recent example had the archers engaging a pack of ghouls at 100 yards, where the range penalties alone would reduce the ghouls vision based Per to 2 or 3.

Does anyone have suggestions for how to run combat with stealthy ranged fighters? I've considered having stealth rolls at a penalty after each shot, treating the archer as "in plain sight" while firing for a +10 to vision, or letting people hone in on the bow fire by sound and the trajectory of the arrows even if they don't spot the archers until they are right on top of them.