I suspect that the only way to handle this is for the skin to keep its own variables for pano bounds - ca2MaxImageWidth, for example - and then traverse the album objects in postdir.bsh and generate new slide images if necessary.
I don't (yet) have trouble passing the maxImageWidth value. The trouble is with the pano and pano360 booleans only. This code (the one with the radio buttons) was just for fun and to test whether i could do it actually.
The latest production version of CA2 has one "Panoramic image" checkbox and one text field only, and - keep finger crossed, I will have to test it again now... - worked flawlessly so far.