Tony,
quote "It seems to me that the Captain could have done a better job of keeping the F/O in the loop." Unquote.
If the captain asks for a 30 mile offset, you either ask for a 30 mile offset or question him about the distance, time permitting. If, like in this example, he changes the request on his own accord, it is plain insubordinance.
As a captain I would have steered the airplane to a 30 mile offset and ask him to coordinate such with ATC.
While on the said course, and safe from cb's, we would have a little discussion about the matter. And I mean discussion, not a lecture.