Open your original texture (Left) in an image editor, and select or mask all the areas you want to be reflective. Using layers for this is helpful. Fill the areas you want to be reflective with white, and the rest of the image with black (Middle). This is just like making a transmap. In a transmap your white areas are visible and your black areas are not. Here your white areas are reflective and your black ones are not. As an optional third step (Right), you can fill the reflective areas on your original map with a solid color similar to the color you will be reflecting. This will prevent the texture from shining through the reflection, but won't always be what you need or want. In my case I was going to reflect a gold color, so I filled the reflective areas with a pale yellow. More to come...