Boot windows bios from second internal drive MBP Mid 2012
Below is a excerpt From page 6 of the Boot Camp Installation &amp; Setup Guide (Copyright 2011). These instructions do change significantly with the next release of the Boot Camp Installation &amp; Setup Guide (Copyright 2013).


  If you have a Mac Pro with more than one internal disk and you want to install Boot Camp on a disk that isn’t in the first hard drive bay, remove the drives in the lower numbered bays. You can reinstall the drives after you install Boot Camp.


Back in 2011, all Macs were still BIOS booting Windows. Although the excerpt does not explicitly say Mac Pro's where the only models that could BIOS boot from a second internal drive, this was already generally known to be true. So, the answer to your question is your 2012 MBP can not natively BIOS boot from the second internal drive.

rEFInd is a Boot Manager. This means rEFInd does not actually boot operating systems. Instead, rEFInd saves information in the nvram. The Mac firmware reads this information to determine which operating system to load. The means rEFInd can to be directly used to BIOS boot windows from a second internal drive.

On the other hand, GRUB 2 is a boot loader. You may be able to BIOS boot GRUB on the primary drive and configure GRUB to boot Windows on the second internal drive.