make post process on child actor camera

hey all.

basically what im doing is a standard FPS aim down sights feature.
im using a set view target with blend to switch between the fps camera and the gun camera which is a child of the gun.

it works absolutely fine except i want a vignette and a DOF on the child camera and i need this effect to blend in and out, not just pop in with the view blend completes.

i can make the vignette intensity grow on a timeline from the fps camera, but i cant alter the post effects in reverse from a child camera, any way around this?