This script+dockerfile will create a patched boot2docker.iso with support for vboxsf. That means you can then use docker volume mapping just like you're used to when running docker in linux.
It uses the boot2docker/boot2docker image from Docker Hub according to the official patching guide (https://github.com/boot2docker/boot2docker/blob/master/doc/BUILD.md#making-your-own-customised-boot2docker-iso), downloads and installs the VBoxGuestAdditions from Virtualbox. Then it adds a shared volume to Virtualbox that maps /Users on your host machine to /Users in the boot2docker vm.
git clone https://github.com/larsla/boot2docker_vboxsf.git
cd boot2docker_vboxsf
vi Dockerfile # Update VBOX_VERSION with the version of VirtualBox you're running
bash update.sh
$ cd /Users/larsla/Code/my_project
$ docker run -i -t -v $PWD:/my_project base bash
root@24e68e83c74f:/# df -h
Filesystem Size Used Avail Use% Mounted on
rootfs 19G 2.6G 15G 15% /
none 19G 2.6G 15G 15% /
tmpfs 501M 0 501M 0% /dev
shm 64M 0 64M 0% /dev/shm
/dev/sda1 19G 2.6G 15G 15% /.dockerinit
/dev/sda1 19G 2.6G 15G 15% /etc/resolv.conf
/dev/sda1 19G 2.6G 15G 15% /etc/hostname
/dev/sda1 19G 2.6G 15G 15% /etc/hosts
none 466G 195G 271G 42% /my_project
tmpfs 501M 0 501M 0% /proc/kcore
root@24e68e83c74f:/# ls /my_project
this_is_my_project.txt