Adding Fedora15 to F16alpha grub2 menu

[Petrus de Calguarium]

I have installed F16α and with it grub2 to the MBR of /dev/sda. I am 
experimenting happily with F16, but I am unable to add F15 to the 
grub2 boot menu.

I have edited /etc/grub.d/40_custom and run grub2-mkconfig -o 
/boot/grub2/grub.cfg, but my F15 entry never shows up in the menu, 
even though it is in grub.cfg.

When I start the computer and select the (c)ommand line in grub, I am 
able to enter:

set root=(hd0,7)
linux /boot/vmlinuz-2.6.40.3-0.fc15.x86_64 root=/dev/sda7 ro quiet etc 
etc etc etc etc rd.xxxx=0 etc etc etc
initrd /boot/initramfs-2.6.40.3-0.fc15.x86_64.img

and then type boot, I am able to boot F15 without problem.

Entering the same into the grub.cfg file doesn't work.

How can I get a F15 menu entry in grub.cfg?