Sales Tax SDTAX1 being pulled from Shipping Branch SDMCU - Would like from SDEMCU

We are shipping products from a central warehouse where the Item branch is setup as taxable F4102.IBTAX1 = Y.  However when shipping to certain countries i.e. UK some of the products are TAX exempt.  Does anyone know if there is a way to default the Tax flag from the header branch item i.e. from the SDEMCU of the order.

Example;

SDMCU = 10

SDEMCU = 20

Currently the SDTAX1 is being pulled from SDMCU = 10  but would like to pull it from SDEMCU = 20

Thanks