Hmm. Just to see if I could do it, I did it.

I cannot imagine why you want to do this, but here's how I did it.

I have a free object in my web site called GenIBL. I used it to convert the free Doge palace HDR equirectangular image into an IBL.

I then rendered with the IBL and also with the EnvSphere. They produced roughly equivalent light after tweaking the IBL settings.

Here is the setup using a wide-angle camera.

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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)