We don't support it directly, I agree.
Nevertheless, one tip does give a good results. With internal editor, change all focals to 2000mm.
With such a focal length, the image represented in rotation model (the one that is coded in autopano) looks like a plane as the sphere is so big that the curve of it doesn't look curved.
It works quite well.
Yes, that does work reasonably well I agree. But there are a few quirks, especially when the panorama gets large.
I was just suggesting in an upcoming release to perhaps include a dedicated feature. If you can, it would be great. Thanks!