ID will not accept negative numbers for mark offsets in the export or print dialogs, so you either have to add them manually, perhaps using the cropmarks sample script, or do what I used to do when I worked in a large format house: add a full outline for the cut line.
I am not familiar with the cropmarks sample script. Can you provide me information on how this script can be implemented. Thanks in advance.
Before (showing the upper left edge of the page; the helper rectangle is obscuring the page edges):
After (helper rectangle removed after running the script):
Thank you. Works great.