Conditional ON DUPLICATE KEY UPDATE (Update only if certain condition is true)

Question

I have the following query being used:

INSERT INTO userlist (username, lastupdate, programruncount, ip)
VALUES (:username, NOW(), 1, :ip)
ON DUPLICATE KEY UPDATE
lastupdate = NOW(), programruncount = programruncount + 1, ip = :ip;

However, I also want to make the ON DUPLICATE KEY UPDATE conditional, so it will do the following:

• IF lastupdate was less than 20 minutes ago (lastupdate > NOW() - INTERVAL 20 MINUTE).
• True: Update lastupdate = NOW(), add one to programruncount and then update ip = :ip.
• False: All fields should be left the same.

I am not really sure how I would do this but after looking around, I tried using an IF Statement in the ON DUPLICATE KEY UPDATE part.

INSERT INTO userlist (username, lastupdate, programruncount, ip)
VALUES ("testuser", NOW(), "1", "127.0.0.1")
ON DUPLICATE KEY UPDATE
IF(lastupdate > NOW() - INTERVAL 20 MINUTE, VALUES(lastupdate, programruncount + 1),
lastupdate, programruncount);

However I am getting the following error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF(lastupdate > NOW() - INTERVAL 20 MINUTE, VALUES(lastupdate, programruncount +' at line 6