August 13, 2010 at 06:25
The feature is not supported. The reason is following: left and right insets are values, which define final HTML-to-PDF scale factor. If they change itself from page to page, it will cause the corresponding scale changes, which is not desired.
If you need to change only top and bottom insets/margins, you may achieve that with empty inline headers/footers. See and tags and their scope attribute.