I've heard about this as well. Only can't remember where and now you got me curious as Ayu history interests me a lot. There are some mentions about a TVCM at the following page (found these very quickly, therefore there are probably a lot more info out there):
http://www.hanamoku.jp/wikipedia/浜崎あゆみ
http://www.10bai.com/r/hamaayu.html
http://www.ayuloveayu.com/history.html
I wonder if the pic in the second link is from the CM? Perhaps
Delirium-Zer0 knows more about it, she tends to know a lot!
EDIT: Could it be this CM:
http://jp.youtube.com/watch?v=GlD7IeWBA2Q?