Applying pixel shader to content of OpenGLView

I have an OpenGLView which includes some content as follows:

<OpenGLView HasRenderLoop="True">
        <Map />
</OpenGLView>

In the render loop callback I would like to apply a pixel shader effect to the OpenGLView Content (in this case a Map control).

Is this possible? Is there a way to get a bitmap from the OpenGLView content?

If not, any ideas on how this could be implemented - perhaps as a custom ContentView renderer that allows grabbing of the pixels?