Rikk, I see what you mean, but the nice thing about using keywords is if two or more cars are prominent in the shot, I can just check two or more boxes. Also, selecting from a big dropdown, while better than nothing, would probably be a bit tedious.
Mark, I have LR/Transporter, but unless I'm missing something, it will only export to a file and the client can only use embedded caption metadata. Your other option might be viable, however...
John! Awesome! Your plugin does exactly what I need! Thank you! Is it still really limited to only 3' uses though? That will hopefully get me through this event if I don't screw up too much, but I, too, would be happy to pay for a full version.