DrawingContext does not support ShaderEffect.
Using DrawingContext in OnRender() method of adorner, we can Push effect using PushEffect() method. But the strange thing is that DrawingContext.PushEffect() does not support ShaderEffect. All it supports is BitmapEffect :(
So if you don't want to use BitmapEffect as it is obsolete now then you DrawingContext wouldn't be of much use to you.
If you want to study about ShaderEffect, you can refer this post: