Booting FreeBSD 5.x from an extended partition?

[Nate Lawson]

I appreciate Grub -- great utility.  I am successfully booting Windows and
FreeBSD 5.x on primary partitions and Linux in a logical partition but am
unable to boot FreeBSD 5.x on a logical partition.

This works for FreeBSD on a primary partition:
root (hd0,3,a)
kernel /boot/loader

Doing this fails:
root (hd0,5,a)   # second logical partition in extended partition

The error given is:
Filesystem type unknown, partition type 0xa5

Booting into the primary partition version of FreeBSD allows me to mount
/dev/ad0s6a (the equivalent to the above root line) just fine. Just in
case, I tried with it formatted for UFS1 and UFS2.  Both give the same
error.  Ideas?

-Nate