Migrating SqlServer (2008) Named Instances To Schemas?

I currently have a sofware with 80 customers.All share the same database structure, when data are differents.We got 5 database for each customer.Today, we have named instances, so the program is accessing to Bdd with something like :

Connect to 127.0.0.1/CUSTOMER1
select * from base1..table1

Now, we need to change, we got many instances.The idea is to have unique SQLSERVER instance, obviously i want to avoid changing the code (VB.NET).Just tried to play with schemas and users, seems to be an option, but since the schema is under the database, in can't make it works :

Connect to 127.0.0.1/GLOBAL_INSTANCE as specific user (customer1)
select * from base1..table1 -> error @ this point

When THIS works :

Connect to 127.0.0.1/GLOBAL_INSTANCE as specific user (customer1)
Use Base1
select * from base1..table1 / or select * from table1

I can easily script some user or schema creation, and change connection strings for all customers, but i can't really change All requests: huge number.