There's an example for modelformset_factory that uses the formset argument and while you might be able to infer a similar technique will work for inlineformset_factory since the docs say "Inline formsets is a small abstraction layer on top of model formsets", I agree an example could be helpful. I'm not sure it should be specific to the "Overriding clean()" section though, since the formset argument is useful for other cases as well.
If you could offer a patch, I'll be happy to review and commit it. Thanks!