Adding a custom database connection

Hi, I'm a new nopCommerce user and I'm trying to extend some functionality related to Customers.
What I want to achieve is to populate the data of a customer to a table in a custom database when a Customer is created or updated.

I'm using a custom NopCommerce code v2.4 wich I can not upgrade at this moment.

I have the following scenario:

1- NopCommerce inserts a Customer.
2- I created an extension class for Customer, extended the Create(Customer customer) method and call to a Foo() method wich writes in disk some text (just for testing proporse). I call the Foo method in Customer controller in the create method

This part is working great.

What I did after that is adding a new connection to my custom database. I added a new ADO.NET Entity Data Model to Nop.Core project ('CustomDb.edmx') and I instantiated this in my CustomerExtension class.
Then at execution it raises an error 'Not found conceptual model for Nop.Core.mytablename '
My guess is that NopCommerce is trying to dinamically map my table to some model entity in my project.

Is it possible to achieve this without creating a mapping class for my table?

If the last is not possible, could someone write the following steps to make the mapping work?

Thanks in advance !