How run in a chroot jail not as root and without sudo?

Question

I'm setting up a minimal chroot and want to avoid having sudo or su in it but still run the my processes as non-root. This is a bit of a trick as chroot requiers root. I could write a program that does this that would look something like:

uid = LookupUser(args[username])  // no /etc/passwd in jail
chroot(args[newroot])
cd("/")
setuids(uid)
execve(args[exe:])

Is that my best bet or is there a standard tool that does that for me?

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I rolled my own here:

Answer 1

fakechroot, in combination with fakeroot, will allow you to do this. They'll make all programs that are running act as if they're being run in a chroot as root but they'll actually be running as you.

See also fakechroot's man page.