When I send a destination to my car via MapQuest. I let sync dial the number and connect. Then it tells me about the destination that was sent and it asks me if I want directions to that destination. If I tell it yes it gives me the directions (it downloads the destination and calculates a route).
So that is not a direct answer to your question about a command to download the destination but I have never had to use a command to download a destination.
So when it dials the number do you let it dial and connect?