I am using docker toolbox on Windows 7 to run docker. (docker version 1.9.1)
As it turns out, the docker machine creates its VM at C:\\Users\\username\\.docker\\mach
Put these two commands when running docker quick start terminal.
I suppose that your new location is "D:\docker" and your new machine name is "docker1"
export MACHINE_STORAGE_PATH=D:\\docker
docker-machine create --driver=virtualbox docker1
This should create a new machine with specified name in your new location.