Thanks to the Engineering Walden, you can now get CentOS 6 set up in a FreeBSD 10.2 jail. Follow the link for the full tutorial.
CentOS 6! In a jail on the FreeBSD 10.2 kernel! THAT’S EFFING AWESOME.
I just got this up and running after some hours spent cobbling together instructions from the various sources to which I link below, and then troubleshooting some issues (one of which is listed at the bottom for anyone else who encounters it), but it works.