debernardis already pointed it out, and the source also doesn't lie:
http://git.alwaysinnovating.com/cgit...leos/switch.sh

It is just several chroots, which you can already do using Easy Debian. If anything, the hard part comes from having a single kernel that can run both Android stuff and a normal GNU userspace, something that there's little chance it is directly portable to the N900.