If you have grub2 installed.

wubi direct boot on first drive second partition or sda2 or hd0,2

Code:
menuentry "Wubi" {
insmod ntfs
set root=(hd0,2)
loopback loop0 /ubuntu/disks/root.disk
 set root=(loop0)
linux /vmlinuz root=/dev/sda2 loop=/ubuntu/disks/root.disk ro   quiet splash
initrd /initrd.img
}
I have installed grub to NTFS, FAT32 & Linux formatted partitions, so it works just about anywhere.