External Fusion Drive?

I'm in the market for a new Mac and from what I've been told everyone seems to think Fusion Drive is worth it. However, not having the extra money in my budget for Fusion Drive, I was considering using OWC's Data Doubler and a Samsung 840 Pro to make a Fusion Drive in a Mac Mini for $120 cheaper than buying it from Apple. However, it seems Apple has switched the location of the hard drive in the Mac Mini making pretty much all current kits incompatible. I could use a SATA to USB 3 and hook it up that way, so I am wondering if anyone has had any success doing a DIY Fusion Drive with an external drive. Some say it is possible, and some say it isn't. And yes, I understand if the drive becomes unplugged the whole computer stops working, I never plan on moving this machine so portability is not an issue.

TL;DR: Has anyone had success with a DIY Fusion Drive using an external drive?

Thanks for your help!