Rain Rain Rain

I use Blender for the game engine but many of my ideas, which i'm just starting to post, can apply to other render methods. For realtime rain would it be possible to take a quarter resolution snapshot of the render result, and blur it either with a (I'm guessing here cause I don't yet know much about the render methods in programming) quick Gaussian blur or a better smooth blur depending on the host computer's capabilities and then overlay this on the scene with an alpha channel taken from an animated streak rain pattern. I mainly think of this for night scenes but I guess it would work in day scenes too. It could also be used for rain drops on glass e.g. a windscreen, by applying a fake beveled texture in splat shapes to the glass surface. Each of these splats would have a larger proportion of the texture than their own size mapped to them (inverting x and y coordinates) thus mimicking a refractive water drop without any ray processing. Maybe also darkening the rim of the drop and lightening the center but this is getting more complex where the idea was to keep up game speed on my £200 laptop. Do you get me? Imagine a blurred render of your scene and a load of 8 bit grey-scale rain drops, now imagine each rain drop colored with the blur texture inverted on y and x from a sizable circle around it. If you don't get me please feel free to ask in a comment. Thanks. P.S. Note that the picture I used is a photograph and is intended to be used as an example of the method not the result, the result would display a full resolution clear image between all the drops. Thanks.