The documentation is sketchy, but I don't see anything suggesting this is designed to allow you to implement filters. Rather, it is designed to implement entire web access systems, perhaps to support a new kind of browser which would do everything. The driver would be expected to do everything or fail (and, being the only browser, Acrobat would give up).
To work as a filter you'd need to be able to get at the existing driver definitions and call them, and I can't see any way to do that.
I may be completely misunderstanding. Have you seen anything suggesting it is supposed to be used to implement a filter?
If you want oversight of the weblink process, it seems it might be possible by subclassing the standard action handler, but I haven't examined it in detail.