Hey ashley,
So i'm not entirely sure if it's possible at all. The reason being that FiveM uses GTA's combat system, and there's only one view when using a sniper, which is stood upright. I doubt that this is possible and may be something we can look into the possibility of in the eventual future when the backlog clears up, however at this exact moment it's not going to make its way on to the to-do list.