You can do it with 2 disks. You just need to unplug the Linux disk while installing windows. If you then make Linux the primary boot disk in bios, grub re-maps

You can do it with 2 disks. You just need to unplug the Linux disk while installing windows. If you then make Linux the primary boot disk in bios, grub re-maps the drives so when booting Windows, it thinks it is the primary drive and never re-writes the Linux boot loader. I did that for years without issue.