This is something I had to do in AOOI to get the /boot partition (a RAID-1) bootable. The following forces grub to be written to each disk. This is a batch mode version, you just paste this right into the command line, or inside a script. If you want to run it manually, take out --batch and everything after it.
/sbin/grub --batch <<EOF root (hd0,0) setup (hd0) root (hd1,0) setup (hd1) quit EOF