PagingNavigation has two actions in its onBeforeRender implementation:
setDefaultModel(new Model<Integer>((int)Math.max(Integer.MAX_VALUE, pageable.getPageCount())));
Building my own PagingNavigation extending PagingNavigation, not being able to retrieve the start index before onBeforeRender, forces me to put a lot of logical code into my own onBeforeRender implementation.
So there's a valid workaround, but I'd expect this to work from onConfigure also, maybe even from onInitialize.
As far as I can see it should be possible to call the two methods earlier than onBeforeRender, however I might be missing the "big picture" and oversee some side effects this could cause.