User tables in different database

Hi.

I know I can define the users tables on the wp-config, but I need to have them in a database aside of the main database.

In my work, we going to make different webs on different engines, but with common users on them. I know WP have the multisite option, but to mantain the privacy and security of the users data, we need to have that data on a different database. So, there´s a way to have those tables on a database aside of the main?

Thanks for your time, and sorry about my english.