the only way to clarify the responsibilities and to prevent the pilot from altering his avoidance heading again is by transmitting:
"continue present heading as radar heading", cause avoiding CBs is legally considered "own navigation" of a pilot.
"Fly present heading vector for traffic" does it nicely with approved phraseology from the book ("the book" in the US being the FAA's 7110.65) for me. Now the aircraft is on an assigined heading.
Dave