Blur & Sharpen > CC Vector Blur does this but you'll need a way to define the curve. You might, for example, create a white/black matte. The transition between white/black would be the "line" along which CC Vector Blur will blur. Use this matte as the Vector Map for the effect. I believe you'll also need to rotate the Blur 90° if you use the Natural mode.
Tweak the Ridge Smoothness and Map Softness as well as the Strength to adjust to your needs.