Non-retina MBP question:

Hey all, I'm looking at buying a non-retina MBP when they're updated with Haswell this Spring. My specific question is about Fusion drive. I plan to get the laptop with the 750GB 7200 rpm hard drive and to add an opti-bay with a 256 GB SSD. Has anyone tried this and discovered whether Fusion Drive is operational when you add an SSD of that size?