Hi Alex, sorry but currently there isn't any mechanism in MoI to alter the PDF page properties, it's fixed at 8.5x11 inch portrait for now. I definitely want to address that in v4 but for now you would need to edit the page size in a 2D vector program like Adobe Illustrator, or use one of the methods described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6522.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=6522.5

- Michael