So you can't make sniper and sneaker at one char, just forget it.So you need at least 300% Sneak skill and "sneaking" perks to be a bit invisible.So sniper needs at least 200% to have efficient chance to hit.So this means you can't do it, because there is not enough skillpoints. Simple, my dear Watson.
When you shoot, you become visible. Doh...
AG 9
no
Shoot, hide, resneak. Repeat.