I'm a bit confused here. The style gets modified on the fly by the DefaultResourceLocator to build relative urls, so once it's out of styles, the references to the graphics have already been modified no?
The style should be usable as is, minus the need to locate the referenced resources and extract them on the file system.
It might be probably be cleaner to have a subclass of DefaultResourceLocator that can be passed to Styles, that would do the job of extracting the files while the parse is happening, this way you'd get the parsed style out, and the references ready the moment the parse ends. Might be quite a bit cleaner than this N-steps style loading.