Take a look at:
CodeSmith 4.x Samples -> Xml -> Entity.cst
This reads in a plain XML file that conforms to EntityMap.xsd and creates a simple class from it.
It's similar to what you're looking for. It may be a good starting point.
Theoretically, you could point an XmlProperty's schema to
the XSD for XSDs.
You would also need
the DTD for XSD and
the DTD for datatypes.
When I try this, though, I get a cryptic error:
There was an error reflecting type '_CodeSmith.pattern'. : There was an error reflecting type '_CodeSmith.element'.
Worst case, I would consider loading your XSD into an XmlDocument in CodeSmith, and using the XmlDocument's properties to drive your template's generation.
Hope this gives you some ideas.