Personally, I don't have a problem if the familiar assists with strengthening the bond after the bond has been created.
One reason I might use in lawyering the answer being no, is that the Familiar Lab Total doesn't explicitly state that an assistant can be used. But the counter to that argument is that the Lab Total on page 94 doesn't included bonuses for assistants, either. Nowhere does it say in the Familiar section that you can't use an assistant. I can certainly see a familiar saying to their magus, "If you do this, this and this, you'll be able to improve the bond, perhaps strengthening one of our weaker cords."