Multisite and wp_users

Hello,

we have originally started to use MultiSite in order to centralize administration and updates management for our clients, which are completely separate companies.

We have, after some time, encountered the following problem: As “wp_users” table is shared among all sites, if somebody registers on one of the sites and would then want to register to another one, it would tell him that his username / e-mail address is already used, which would pretty much confuse him.

This is also problem for certain commerce plugins, like WooCommerce, which writes customers into wp_users table and given that each site would sell 100 products a month, it would make the table quite a mess very fast.

Is there any way how to override this shared wp_users or any other solution suggested?