Here is a screen shot of part of the animating shader. You can see I'm using the Frame_Number (upper right) to drive the rotation. If we changed that to a constant, you could type in any rotation you want.

The Image_Map node in the upper left, called Angular_Map, is the resulting modified image to be used in the IBL.

I added another Image_Map, called Panoramic_Image, that is showing the unmodified texture file, without any math applied.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)