This actually isn't too difficult, just a matter of understanding schedule:
Set up DHW in the DD wizard (on for all months of the year)
Then, go to detailed mode, and create/copy a daily fraction schedule with all hours zero
Create a weekly schedule with all days using the previous made schedule
Edit the annual ext ltg schedule and set the months that you want to be off using the previous weekly schedule
Don't forget to go to the Utility/Economics module and select the electric meter and check out the "direct loads" tab to verify that you have the correct maximum wattage.
This actually isn't too difficult, just a matter of understanding schedule:
I hope that solves the dilemma.