Is there a way to save the current frame without rendering the hole thing again?

Is there any way to save the current frame (without UI would be nice) without rerendering everything? I need to make a custom glass material (with fake refraction) for mobile and I wand to use the last rendered frame as albedo mapped in screen space to which I can apply some distort and other transformations. It would also be nice if I could sample a certain mip from that rendered frame to simulate a blurry refraction. It is basically an emissive material with the emissive texture mapped in screen space. Something like this photoshop fake:

This would be really nice and cheap (performance-wise).

I’d be interested in that too!