Comment 7 for bug 217348

On second thought, using:

find --set-root --relative=/ubuntu/disks /ubuntu/disks/boot/grub/menu.lst

is more generic and even if setting the root is superfluous in the case of Wubi the setup above might be useful where the grub menu is used directly without going through the embedded menu.lst. The disadvantage is that using find --relative requires upgrading the grub package (which will probably be required anyway because of other patches).

--- grub-installer 2008-04-28 16:21:48.519362000 +0100
+++ grub-installer.new 2008-04-28 16:26:37.285702000 +0100
@@ -857,7 +857,7 @@
 fi

if db_get grub-installer/bootdev_directory && [ "$RET" ]; then
- sed -i "/^# groot=/s:).*:)$RET:" $ROOT/boot/grub/$menu_file
+ sed -i "s:^# groot=:# groot=find --set-root --relative=$RET $RET/boot/grub/$menu_file:" $ROOT/boot/grub/$menu_file
        need_update_grub=1
 fi

A variation of the above involves looking for a UUID file as opposed to looking for menu.lst as suggested by Colin.