The wizard will let you proceed with the import, but if you are using "insert script" method any rows with columns > 4000 characters will fail to import. I can successfully import clob columns using "insert" method. If you encounter errors during the import, a bad file will be created which contains a script to load the error rows. However, if the error is in a row that contains a clob with > 4000 characters, you will not be able to use this script to complete the load. My recommendation would be to test the import with a copy of your table first.
Can you build an Oracle directory on the server and move the file to that network location? If so, then you could build an external table and reference the columns that you want to access via a select/insert into your table..
Or simpler yet, use SQL Loader to load the file into your table, you'll just have to define the file layout for SQL Loader to grab the file contents..