Well, it shouldn't be too hard.
Simply export your UV map as a screenshot into PS, and color in all the areas in you want shiny white and all the areas (objects) you want dull black (or varying shades of grey if you get fancy). Then plug that image as a texture into the specular attribute of your blinn. It will read black as zero specular (no shininess) and white as highly specular (very shiny). White would equal 1, which would probably be too much.
The same goes for reflectivity, but a little goes a really long way, so you'd probably want everything quite dark, and the sand to be black for that map/texture.
Does that help? If you need more details (like plugging a texture file into the attribute) just ask.
Basically, it's the same process as making a color texture, except instead of color, you're making areas of dark and light which provide the shiny and non-shiny areas.