Multiple users for one google/facebook account

So let me give you some context first, I’ve a multi tenant site where the tenant is identified in the URL.
The people should be able to enter a tenant and register/login with facebook or goole but the problem is when they’ve already registered in another tenant.

Ideally I’d like to allow the user to register multiple times, creating a different user each time probably attaching the tenant name to the email to avoid duplicated email errors. I achieved this using the Accounts.onCreateUser hook but the problem comes when they try to login in another tenant, I need to check the URL to see which tenant the user’s trying to enter so I can choose which user (associated to this service) I must login.

I tried Accounts.validateLoginAttempt hook without luck. I’d like to know if somebody has done something like this or any though you have really. I know another way which is create a single user and somehow give him access to different tenants, but if the multiple users thing works would be great