Here's the plan:
Create an ant task in woden build.xml to download the wsdl20 schema, xml schema and dtd files directly from w3c (this is currently done in downloads/w3c/build.xml target "copy-wsdl-xsd"). This task will be used as part of the woden.jar build process. In addition, a fixed-content URI Resolver Catalog file ("system.catalog"), containing resolves for each of those files, to the local destination within woden.jar (or the development environment). The files will appear in directory /schema in woden.jar. In a development environment (ie no woden.jar), the ant task would need be run manually to create /schema and contents under (for example) eclipse project root. Omitting this step is non-destructive - if the location schema files are not found when woden is executed, it will simply look for them in the regular w3c location on the net.
I think the w3c build.xml could be changed to reference the schema embedded into the woden.jar the test-suite uses, rather than download its own set as it does currently.
The existence of this new system ("hidden") catalog is in addition to the traditional catalog file (now called the "user catalog"). The system catalog is loaded first followed by the user catalog, which may override system catalog entries if so required.
I have a working proof-of-concept for the code changes in my sandbox and am working on the ant task changes. However, I'd like to take any questions / possible concerns before going too much further.