update address-dependent email field on save of BP

We have a requirement to update the address-dependent email field from the address-independent email field upon saving a Business Partner.

I've been working on the 'BUPA_ADDR_UPDATE' BADi but am having no luck with it so far. I have managed to retrieve the data in the address-independent email field using the 'BUPA_CENTRAL_GET_DETAIL' Function Module but as yet have not been able to do the update of the address-dependent email field.

Can anyone offer any guidance please ?

thanks,

Malcolm.