It's beyond the scope of current EyeFinity. If it just render the whole area and used only portion of it, you're talking about a bit of a nasty performanace hit. Frankly, I wish it could do this stuff, because it would allow for some very advanced simpit display setups. I'm not holding my breath on this option though because it's way too specialized for a large enough userbase to budget for it.
My suggestion is if you do 5 displays, go 5 1920x1080 in portrait mode in a horizontal span once the EyeFinity6 is out.
On the other hand...you can trick the EyeFinity6 into doing a span of 3 with one above OR one below. Put 2 dummy plugs on the outer ports to simulate the displays. Google dummy plug to understand how to make them. One would think you could make them out of the DP-to-VGA converters. People use dummy plugs a lot with Vista and Folding@Home.