Since there are no other answers I will attempt a partial one. I used to print 13x40 panos on a 2200 from Windows, but I don't think I ever set up a custom paper size, but rather used the "Roll Paper" source setting
I tried to do this, but I don't think it is going to work. The roll paper I have is 8.3" wide. Here are the roll choices from the "Paper Size" pulldown in the "Page Setup" dialog that are anywhere near 8" wide: (in this case the symbol -> means a secondary pull down)
A4 -> A4 (Roll Paper)
A4 -> A4 (Roll Paper - Borderless)
A4 -> A4 (Manual - Roll)
A4 -> A4 (Manual - Roll(Borderless))
A4 (Roll Paper - Borderless Banner)
20 x 25cm (8 x 10in) -> 20 x 25cm (8 x 10in) (Roll Paper)
20 x 25cm (8 x 10in) -> 20 x 25cm (8 x 10in) (Roll Paper - Borderless)
20 x 25cm (8 x 10in) (Roll Paper - Borderless Banner)
US Letter -> US Letter (Roll Paper)
US Letter -> US Letter (Roll Paper - Borderless)
US Letter -> US Letter (Manual - Roll)
US Letter -> US Letter (Manual - Roll(Borderless))
US Letter (Roll Paper - Borderless Banner)
When I select any of these paper sizes, there is a distinct width and length to the selection. For example the 20 x 25cm is, well 20x25cm and the US Letter is 8.5x11". In Photoshop the print dialog then shows as if that were the paper size and truncates the panorama to that size. Further, the print preview window shows the same.
Is this not what you were suggesting? Or is the "source setting" you describe something different than "Paper Size"?
--Jim--