Speak for + noun etc

I've sometimes come across the prepositional verb 'speak for', meaning 'be a clear sign of' in such sentences as 'The regular attendance speaks for the success of the course', etc A student of mine has asked me whether we can also say 'That speaks for how difficult it is to ...', that is, 'speak for' followed by a noun phrase headed by a wh-word.
What does everybody think? thanks in advance!