It's almost as much fun as getting them to recognize that my home mail server is not a bulk sender, however even after filling out their form they still continue to block me.
In all seriousness my only suggestion is to fill this form out repeatedly. My general experience is that they read 1 of 10 abuse reports... so... http://help.yahoo.com/l/us/yahoo/smallbusiness/abuse.html
Also found they respond quicker (if at all) if you flag it as "illegal activity".
Good luck!