Yeah you are right which is why it would require a real-time generation of a cube map to use as the environment map for the object. Actually using render to texture methods I'm fairly sure I can come up with at least reflecting the skybox or backdrop. Reflecting planets is a whole nother ballgame because I would prob have to cast rays towards the planet - find out what I hit and what texel in the plane texture I hit.....etc, etc. Basically ray trace the stupid thing which is totally out of the question. If I want to do this I might go with the cube map reflection along with imposters created from planet/laser/animation images. Blending the environment map or cube map with the imposters textures using render to texture just might work.
