SqlMapper.DataSource = new PerUserDataSource( SqlMapper.DataSource );

public class PerUserDataSource : DataSource
{
	IDataSource _innerDataSource = null;

	public PerUserDataSource( IDataSource innerDataSource)
	{
		_innerDataSource = innerDataSource;
	}

	public override string ConnectionString
	{
		get
		{
			// build the connectionstring base on the user session setting
			HttpContext currentContext = HttpContext.Current;
			string connectionString = "data source=10.1.2.3;database=DBTest;user id=#userid#;password=#password#;";
			return connectionString.Replace(currentContext.Session["userid"]).Replace(currentContext.Session["password"]);
		}
		set { /* */ }
	}

	public override IDbProvider DbProvider
	{
		get { return _innerDataSource.DbProvider ; }
		set {  /* */  }
	}

         /* ... */

}