There's one other way it might be possible, and you're probably the best person to know.
If the pages were in a single category with simple names (like deleted:1 to deleted:1000), is it possible to build a robot to call the correct Ajax/Javascript functions to delete them?
Otherwise, would the dev team consider providing a manual method of deleting a whole category with a single defined name? I know the reason they don't want to is that people will do it by accident, but if the category was "trash:" and the manual interface was "Permanently Delete Trash", and asked twice if you were sure, surely that should be sufficient?