How do I give a texture a dark halo? I have an image with an alpha channel that I am using for a texture.  Right now I just use its alpha channel (that's the only thing checked in the influence panel).

I'd like to give it a "halo"/border.  Consider the following image where I take the outline of japan (from http://en.wikipedia.org/wiki/Template:Japan_football_clubs_map_2011), and give it a black border (this uses an intermediate image from the compositor of a separate scene, very awkward):



My first instinct is to create a second plane underneath with a second version of the texture where I dilate (add pixels around the edge, ⟏ for those of you familiar with Image Algebra) the alpha channel for a dark material.  Unfortunately, I can't seem to find a node which performs dilation in the texture Node Editor.

I welcome suggestions of how to achieve this effect using blender.  (I am using BI, but if you want to answer with a screenshot of a node setup for Cycles I won't complain).
Use a Dilate/Erode node on the alpha channel in the compositor




with background the node setup would be something like this: