Installing Boot Camp on Fusion Drive

I have a 2012 Unibody MacBook Pro that is currently setup with a fusion drive. It has a 120GB SSD in the HDD bay and the original 750GB HDD in the optical bay. When trying to install, I get the error, "Windows cannot be installed to this disk. This computer's hardware may not support booting to this disk. Ensure that the disk's controller is enabled in the computer's BIOS menu." I know that this is because Windows won't install to the "external" optical drive slot, is there a way to work around this? I don't think I can just stick the HDD in the HDD bay since both drives are linked as a fusion. Am I able to swap the disk positions without issue?

Also, as a side note, the total size of my fusion drive is 878GB, yet Boot Camp Assistant shows it as 749GB. So when I partitioned the BOOTCAMP partition as 250GB, it actually created a 359GB partition.