For me the survey that gets send out after warranty work really gets people's attention. At least the dealerships I was dealing with all wanted 10/10 scores, and there was a field in the survey that says some thing like 'do you want bmw usa to contact you regarding your response to this survey.' Got an email from BMW USA customer relations within 2 weeks.
Edit: Got my CPO 335i lemoned in California
Here's the email as direct response to the survey, hope this helps:
Dear FirstName LastName,
Thank you for completing your recent survey response to BMW of Mountain View.
As you requested, a BMW Customer Relations Representative will contact you soon to discuss your comments.
To best assist you, please reply to this e-mail and provide us with:
1) A brief description of any points you'd like to discuss which are not
referenced in your survey.
2) Your daytime telephone number.
The BMW Customer Relations team is available to discuss any immediate questions or concerns you may have. Please feel free to call us at 1-800-831-1117, Monday through Friday, from 9:00 a.m. to 9:00 p.m., Eastern Standard Time. If you’re interested in up to date information about BMW models and accessories, you can visit us at www.bmwusa.com.
Thanks for being part of the BMW family.
Your BMW Customer Relations Team