Oledb

I am not sure if I realy understand your wish. It is possible to use the OleDbCommand to access a SQL Server. You have to use a bit other connectionstring. Have a look a www.connectionstrings.com.

Or do you want to use a SQLCommand for a SQLDatabase and a OleDbCommand for e.g. Access? Therefore you can use code as follows:

var settings = ConfigurationManager.ConnectionStrings[connectionKey];
var connection = DbProviderFactories.GetFactory( settings.ProviderName).CreateConnection();
connection.ConnectionString = settings.ConnectionString;

Therefore use the app.config to configure the database.