Limit sync'ed address book entries to bluetooth car-kit
Please note, this solution will work on SOME Android phones, but not all of them. 

As of right now your best bet is to make a group. Go to Contacts or People (depends on phone), view your groups, and then create a new one (usually done by selecting menu and then Add Group. Then add the contacts you want to that group (it might be easiest to go online from a computer and do this.

Then go into the settings of your groups or from the main contact screen and see if you can only show that group as visible.  On my phone I cannot select individual groups to show and not show. But I think other Android phones can do this. Look for a "View" option.