I believe you can use a BRF+ rule to determine the Sold-to Party BP.
You can adjust the BRF Rule Service Team to Sold-to Party. I perfomed this in another implementation to fill the Change manager.
At the end, create an action based on SMIN_STD_FIND_TEAM_SEND_EMAIL (from SMIN) and change the parameter PARTNER_FCT to 00000001. Should be work (i never tried before with Sold to party, but i believe will work 
Best Regards Issac