I'm aware of the need to match vehicle types in relation to luggage quantity ; but other than that (and speaking personally), I wouldn't feel comfortable troubling a CD supplier with a request for a specific car - if only because I imagine they have enough on their plate already sorting out their various commitments and scheduling etc etc.
Mind you, I'm often half asleep when the car arrives to pick me up and can't honestly say I'd be bothered if they came in a lorry - as long as I get to where I need to be in good time ^