I am blessed, I have two really good sleepers. They will stir when you move them but 99% of the time they do not wake. I can move them from baby carrier/sling to pram to car seat to cot, ect, ect.

I really believe thats its a child by child thing, but here's what I do:

I very carefully and slowly ease my hands under him and try to keep him in the same position he fell asleep in. I use my hands and arms to keep that contact he had with the car seat/pram ect.

*ETA* I've never had to leave my car running or put music on to transfer, but I guess it's worth a try

Good Luck xx