Is GL_SAMPLE_SHADING possible in Unity?

Hi,

I'd like to implement deferred MSAA as per this excellent CryEngine 3 presentation, but my game is using OpenGL for consistency's sake between Windows, Mac and Linux, so for best results I need to enable GL_SAMPLE_SHADING or access gl_SamplePosition in the shader to enable per-sample fragment shader evaluation.

Is there any way I can do this in Unity?

inb4 workaround:
* just use a bigger render target -> GPU does some smart stuff with MSAA targets to reduce bandwidth, according to Nvidia.

Thanks
Jibb