If these positions are uncontested then there should be no need for a vote. You could hold one as a formality if you choose to, but it shouldn't be neccessary if no one else is vying for these positions.
Ultimately you need people (the board) to be planning stuff for the year now. If you put them off for a future vote then your group will be behind in its planning.
Our PTO meeting in May ended with no one stepping up to take over the full board and the existing officers were either moving out of the district and/or resigning. Since then another group of parents have graciously agreed to serve as the new board for this year and have already cleared this with the principal. My question is since it is stated in the bylaws that we must vote on any new officers, should we vote at the first meeting or can this be waived? The group that has agreed to serve wonder if it is necessary.