Give it a backpack and a selective, gun-mountable tri-pod.
The tri-pod can be set up like a mortar and is shown with the gun you have mounted on your main weapon. There should be a few seconds of animation to deploy the pod.
The player cannot move while using the pod, but the gun has almost no spread and recoil, and (for belt-fed guns only) gains 4 belt ammo belts with 100 rounds.
The machine gunner can be combined with existing obstacles and engineer trenches to build a machine gun nest that is easy to remove and move without a functioning bipod.
