Did you try chainloading grub from SC? You can boot Linux with Windows bootloader if you want, so it shouldn't be impossible with anything else either..
what you do in that case is install the Linux bootloader to /boot partition, then use dd to create an image of the first 512 bytes of that partition (512 first bytes of the disk would be MBR). Then you can configure Windows to use that image file to boot Linux.
Note that GRUB 2 is in development and sooner or later replaces GRUB Legacy.