Probably an easier way to solve this problem is by storing the random words in a temporary table and later extract the values. A stored procedure would be perfect for that.
DELIMITER //
DROP PROCEDURE IF EXISTS sp_jumblewords //
CREATE PROCEDURE sp_jumblewords(no_lines INT)
BEGIN
DROP TABLE IF EXISTS tmp_jumblewords;
CREATE TEMPORARY TABLE tmp_jumblewords (
`word` VARCHAR(340) NOT NULL);
REPEAT
INSERT INTO tmp_jumblewords
SELECT GROUP_CONCAT(f.word SEPARATOR ', ' )
FROM ( SELECT j.word AS word
FROM jumblewords j
ORDER BY RAND()
LIMIT 20) f;
SET no_lines = no_lines - 1;
UNTIL no_lines = 0
END REPEAT;
SELECT * FROM tmp_jumblewords;
END //
DELIMITER ;
CALL sp_jumblewords(20);