If you have not tried this procedure, give it a try. It worked for me on my older Toyota Prius Navigation system to transfer entire groups of contacts to the car.
I exported all of the contacts I wanted to transfer to a .vcf file. I first exported all the contacts to a .vcf file on the phone using the People app (export), but my car only accepted the last phone number for each contact in this .vcf file when I transfered it to the car, but your's might work. Anyway, I used Google GMail on the web which allowed me to export contacts for any group of contacts I had in my Gmail to a .vcf file which I copied this .vcf file on my SDCard.
Downloaded Astro File Manager from the Android market.
Opened Astro File Manager and hit MENU/More/Preferences and select 'Edit File Extensions'.
Selected the 'New Extension' button.
Input 'vcf' (without quotes) as the Extension Name.
Input 'text' (without quotes) as the Mime Type.
Input 'x-vcalendar' (without quotes) as the SubType.
Hit Save.
Now, I backed out until I got to my SDCard file listings, I Long-Pressed the .vcf file on my SDCard, I hit 'Send', I hit 'Bluetooth', I put my car in contact transferring receive mode, and then I finally selected my car system on the phone which transfered the .vcf file with all the contacts to my car.
Good luck.