in case anybody else runs into this, here are some suggestions from another forum
i haven't tried any yet:
Consider using the BROADCAST INVOICE feature (Icon) located on the Sales Invoice screen. This feature will allow you to enter a generic Invoice and then broadcast it to multiple recipients based on your selection criteria presented when you click on the Broadcast Icon.
and
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This may not work for you. But if you don't need a separate ship to address for those customers, you could create a custom invoice that prints the ship to address in the bill to position. Then you could set up their multiple bill to addresses in the ship to addresses/contacts.