Does he have an older sibbling, grandparent or other relative that would be available? Perhaps you could team up with another parent who is in a similar situation and exchange duties.
NOTE: Technically auditions can not be held until after school hours. I know that an audition could be held after school and still be during your working hours, but once school starts I hope you will not find that the auditions are being held at, say, noon on a wednesday.
I will see if anyone else has suggestions.
~Heather