Ok, so maybe I didn't completely figure it out. It appears the option for vertical spacing does not exist in all window options. So, in a fixed window, I still don't know how to get the sash frame to disappear.
RA 2012 x64, Piranesi 6 Pro, Sketchup 8, Windows 7 Pro x64, Intel Core i7, 10GB RAM, ATI Radeon Mobile 5870