Live debian USB stick with debootstrap, squashfs and grub

I want to create my own Debian Live boot stick from a chroot (debootstrap) environment. The root filesystem should be mounted as squashfs and grub should be able to boot the system from a single EFI partition. So far, I have a squashfs image of the chroot environment, vmlinuz and initrd.img on the stick. However, I don't know, how I have to configure grub so that it doesn't boot my local system (tried with: grub-install...) but instead the squashfs of the USB stick.