Usually the first 10 rows of the file are used to decide which type the column is. So if you always use the first row as a dummy with an alphanumeric value, you never go wrong here.
Let me know if that will work for you.
Ronald HensbergenHelp us, help yourself... Post data so we can read and use it: http://www.sqlservercentral.com/articles/Best+Practices/61537/-------------------------------------------------------------------------2+2=5 for significant large values of 2