It would have to be a decision made entirely by the public service without any participation at all by any ministers' staff, because first of all, according to Treasury Board's own policy and the federal government's own statement, ministerial staff act on behalf of ministers. You can't use your staff person as a front and have them do the things you're not allowed to do and then claim that you didn't know.
Finance Minister Morneau has already admitted that he did direct his staff to participate. When the chief of staff of the PMO is involved, as Katie Telford testified that she was and others were, they're acting on behalf of the ministers, so the minister is the one who's found guilty because their staff acts on their behalf.
Of course, there is this concept of plausible deniability. Often ministers try to create that situation, and the staff person is the one who falls on their sword and resigns, and they claim they never knew. In this case, we know that they knew.