@brurpo My hack-ish idea was that you only generate it once somehow. You execute a script that sets a global variable if the sky texture has been generated or not. First time, it will generate it. For all other shaders, it won't, because the global value is now true. Really have no idea if this would work.
@brurpo : I'm not sure this is the "right" solution, but you can execute scripts in shaderfx graphs. There is a ExecuteScript node that takes MEL. This could allow you to generate a texture once on first execution. (shaderfx has some MEL commands to bake a section of the graph, up to a certain graph node to a texture on…