Finally got some time to write a more detailed reply. I looked into slip-seat saddles a while back and here are some products that I found:

Spongy Wonder
http://www.spongywonder.com/

BiSaddle
http://www.bycycleinc.com/

SpiderFlex
http://www.spiderflex.com/

Hobson
http://www.hobsonseats.com/

DDwings
http://www.kefren.com/products.html

Whether or not these work for you depends on your riding style. You mentioned it yourself—the lack of thigh control can be an issue for some. Sheldon Brown, for one, was not a fan. What's more, some of these split seats are either heavy or expensive (or both). That said, I'm sure for the right cyclists these are great products and worth trying out.

If I have to choose an ergonomic saddle, I'd consider Selle An-Atomica (very expensive), Brooks Imperial line (expensive), and Allay (moderate to expensive).