I used a random interior photograph of a room, blurred it, made it black and white, and wrapped it around a sphere in Bryce, then dropped the sphereized version on top of the original background photo and used that as a reflection map. You could also make a sky in bryce (or vue) and make a nice sky, and make a mirror surface sphere to create the reflection map. I got the idea from Kai's Power Tools, which uses sphereized environment maps for the shapeshifter filter, but because most of them are dropped on a black background it created too many variations in the image, so I just made my own. But there are a ton of ways you could do this in photoshop, too, using the sphereize filter, for example. Just experiment. I discovered you can use almost any picture as a reflection map, given proper amounts of blurring. =)