Well, I figured it out. Apparently I didn't understand my own equipment. All I had to do was touch the MFD displays and then DCS recognized them. They were already showing the desktop and my mouse could move into them, but I never did that while DCS was running.
I actually accidentally touch one while I was in the simulation and the two MFDs that were at the bottom of my Center Viewer jumped onto the tablets!
Of course I had to tweak the alignment once I finally got them on the MFDs, but that was easy. I had no idea that I had to touch the screens to get DCS to recognize them.
By the way I was using Deskspace on Kindle Fires if anyone runs into this again.