You can try e-mailing YouTube at 
cacopyright@youtube.com and provide the URL to the video and the user's channel. The auto-response I got back is below.
The other thing you can do is to flag the video as inappropriate under the Spams: scams/fraud category. That's what I did as backup. There's also Spam: mass advertising, which I also flagged.
The flagging is anonymous unlike the commenting.
Thanks for contacting YouTube! You've reached the copyright and DMCA
compliance team. Your message has been received and is now queued for
review. Please note that general help inquiries won't be answered here.
For help with other site-related issues, please visit our Help Center at
http://help.youtube.com. If you wish to report abuse or inappropriate
content, please visit
http://help.youtube.com/support/youtube/bin/topic.py?topic=13044, or if
you feel you have a privacy request, please visit
http://help.youtube.com/support/youtube/bin/answer.py?answer=78346.
If you're requesting removal of a video that is allegedly infringing your
copyright, please make sure that you have provided us with all of the
required information in order to process your complaint. Providing
incomplete information may delay the processing of your claim. For the
requirements of DMCA notification, or if you have questions about our DMCA
policy, please see:
http://www.youtube.com/t/dmca_policy Did you know that YouTube offers copyright owners a tool for submitting
notifications more easily? If there are many videos to be removed, or you
expect to have an ongoing need to remove potentially infringing content
from YouTube, we suggest that you sign up for our Content Verification
Program, which electronically notifies us, removing any room for error,
and significantly increases the speed at which we are able to remove any
infringing content. To sign up for this tool please visit:
http://www.youtube.com/t/copyright_program Regards,
The YouTube Team