If there are more councillors than places on the committee, then in order for it to be democratic, there should be a vote/ballot between councillors to fill the places. This is certainly the case with the parish council that I clerk. There doesn't seem to be any reason as to why the Clerk should be involved in the membership and indeed, I would suggest that this is anti-democratic. After all, the Clerk is an employee of the parish council and not the overlord.
Think about it this way, do parliamentary civil servants decide who is in the Prime Minister's Cabinet?