Oracle SQL Loader - how do I replace embedded CR/LF in data?

Question

Note: this is a revised version of an earlier question

I have a text file that is to be imported into an Oracle table with SQL Loader. However, some rows have a CR/LF in their first column, enclosed by double quotes. Note that the row terminators are also CR/LF.

This is the .ctl file I am using:

LOAD DATA
INFILE 'incoming_data.txt'
CONTINUEIF THIS PRESERVE (1:1) = '"'
INTO TABLE my_table
TRUNCATE
FIELDS TERMINATED BY '|' OPTIONALLY ENCLOSED BY '"'
TRAILING NULLCOLS
(
text_column                     char(150),
date_column                     date 'YYYY-MM-DD HH24:MI:SS',
number_column                   integer external,
another_text_column             char(150) terminated by whitespace
)

This is concatenating the two "partial rows" correctly. However, it concatenates the two portions of the first field without any separator. I would like to insert, say, a slash between the two parts - i.e. replace the original newline in the field's data with a slash.

How do I do that? Something like replace(:text_column,'\n','/') is not working, presumably as the continueif is removing the embedded newline.