To solve this issue on my side, I had to use a combo of what was already proposed there
DECLARE
chunk1 CLOB; chunk2 CLOB; chunk3 CLOB;
BEGIN
chunk1 := 'very long literal part 1';
chunk2 := 'very long literal part 2';
chunk3 := 'very long literal part 3';
INSERT INTO table (MY_CLOB)
SELECT ( chunk1 || chunk2 || chunk3 ) FROM dual;
END;
Hope this helps.