Robin,
No python scripting in ArcScan? Maybe no problem. Think remote sensing of your raster scan or source document image.
I have not tried it, but with a Spatial Analyst license, the included Image Classification has ArcPy modules for supervised classification. They would let you script to achieve the same things that ArcScan does with bimodal rasters. You would probably have to do some training on your images.
Maybe not all the bells and whistles--line weights, annotation breaks and such, but should be able to extract usable polygon features and then convert to polyline if needed.
Also, both the ERDAS Imagine and ITT-Visual ENVI 3rd Party extensions to ArcGIS 10 allow you to script in Python--and they provide a richer set of tools for supervised and unsupervised classification and feature class extraction work flows/geoprocessing--probably effective replacements for ArcScan.
Stuart