Epson Stylus Pro 4000 Reference Manual page 170

1. Select Double-Sided Printing, and select the Folded Booklet.
2. Click Margins. The Margins dialog box appears.
3. Specify the edge of the paper where the binding will be
placed. You can choose from Left, Top, and Right.
Note:
When Portrait is selected as the Orientation setting in the printer
driver, Left or Right binding positions are available. The Top
binding position is supported when Landscape is selected as the
Orientation setting.
170
Printing with Mac OS 8.6 to 9.x