According to the manual the transmission has to come off, because the flywheel must be removed. Bummer.
However, it's possible that the transmission needs to be removed only so that the pan can be slid out to the rear, due to the presence of the lower cross member. If that's the case (someone who has removed the oil pan, please comment), then it stands to reason it's possible to remove the pan alone if you remove that lower cross member.
Obviously, a new lower cross member would need to be fabricated.
Ryan