Select disk (not partition) as boot entry

Hi there,

I have Windows 7 and on another physical hard disk Android x86 installed, booting Windows 7 disk primarily.

When I use the BIOS boot menu (chopping F12 every boot) for booting Android, everything works fine. When I'm trying to boot from an entry in boot manager (depends on what 'boot manager' I selected), I either get "file not found" errors, freezes or instant reboots, but no correctly booting system.

Now my question:
How can I just select the MBR of an other hard disk, no matter what freaking boot manager is installed on it? When I just select a hard disk, but no partition, the "add entry" button turns into gray.

Thanks in advance.