Animate Material with Matinee (on Spline Mesh)

I made a waterfall and river as a landscape spline mesh, then I made a material that lets me make the river flow appear with alpha by a height parameter. Now I want to animate that height parameter like I used to from UE3 with matinee but for some reason that is beyond me it doesn’t work like that anymore in UE4. In UE4 I also have to reference all the static meshes that have that material for it to be animate able while in UE3 you only had to reference the material. But referencing the objects in matinee is impossible with Spline meshes, when I try to select my spline meshes the Matinee editor even automatically closes.

I know matinee in UE4 is more limited and timelines should be used instead for a lot of things but the problem is that I want to animate my material parameter alongside other animation.

Is there any chance I can get this working in matinee?