Two different Prestashop Installation in the same host - shared customer information db

[Bandai]

I will install two different prestashop shop with different products on each shop and different admins, but both shops share the same customer information. Like this:

hxxp://www.mydomain.com/shop1/

hxxp://www.mydomain.com/shop2/

If a customer registers an account in the first shop, the same customer could use the same login information on the second shop. Invoice and all that stuff will remain on the shop where the customer bought the item, no need to integrate this two just the login information and the billing and shipping address.

Has anyone here done this already? Care to share how this can be done?

I'm thinking of changing the Customer.php on one shop, but I don't know how to point it to the other shop's DB. If that is possible at all..