Adding a column to FlatFile Connection Source

I have found many examples of adding columns to a FlatFile ConnectionManager but none seem to work.  I'm using the following:

//Adding a connection to the flatfile source
DTS.ConnectionManager ConnectionFlatFile = package.Connections.Add("FlatFile");

ConnectionFlatFile.ConnectionString = @"C:\Test\RN";
ConnectionFlatFile.Name = "SSIS Connection Manager for Files";
ConnectionFlatFile.Description = "Flat File connection";
ConnectionFlatFile.Properties["ColumnNamesInFirstDataRow"].SetValue(ConnectionFlatFile, false);
ConnectionFlatFile.Properties["Format"].SetValue(ConnectionFlatFile, "FixedWidth");
ConnectionFlatFile.Properties["Unicode"].SetValue(ConnectionFlatFile, 0);
ConnectionFlatFile.Properties["RowDelimiter"].SetValue(ConnectionFlatFile, "{CR}{LF}");
ConnectionFlatFile.Properties["HeaderRowDelimiter"].SetValue(ConnectionFlatFile, "{CR}{LF}");
ConnectionFlatFile.Properties["HeaderRowsToSkip"].SetValue(ConnectionFlatFile, 0);
ConnectionFlatFile.Properties["CodePage"].SetValue(ConnectionFlatFile, 1252);

The line that should add a column is below but the coloumns collection property is not recognized.  What am I missing?

IDTSConnectionManagerFlatFileColumn100 flatFileColumn = ConnectionFlatFile.Columns.Add() as IDTSConnectionManagerFlatFileColumn100;