If you want to exclude a column from being produced, you can "customize" the field (right-click the field within the BOMapper -> Customize Field -> Check "Use Custom Code" -> don't enter anything in the custom code blank.  When the partial class is built, the property will be omitted.

If you mean at runtime, then yes, you can retrieve a subset of the columns from the database because the DataTable's structure is independent of the business object's properties, however, when you want to save a business object, you will need all of the columns present, or you will get an error while saving.