c# external sql server queries

We have a C# application, for some reasons i wont go into we are unable to use Entity Framework.

That being said I still prefer to have parameterized sql statements external from my application code, especially the large ones.  For most small CRUD based options I have just written a simple class to map the objects etc.  

What would be the best way to externalize the sql queries but still allow some dynamic parameters, Ill provide a simple example here

StringBuilder x = new StringBuilder();
x.AppendFormat("select * from Customers where CustomerId = {0}", this.CustomerId);