An unapproved method, but functional is to treat "00000" as the missing third string of characters.
Your manual says for WA Key: ABCDE-FGHIJ-KLMNO-PQRST
I think online play for WA doesn't understand this key, but online play for DC, for normal DOW and all single player modes work just fine. So it's up to you whether you want to just try this, or go through the struggle of talking to THQ.
When everything is absolutely perfect, check it again. Twice.