The release version of Deskscapes 8 (8.1 I think) for Windows 8.1 should in fact allow this when you set it via the OS setting, but not when set via Decor8 (as Decor8 does things differently)
So, I was excited by the new info, and I went thru the effort to set up Windows final release 8.1 and just to be up to date, downloaded the "release version" of Deskscapes 8. Sorry, my experience is, Deskscapes still does not work on the start screen. In fact, it froze on the desktop and start screen after setting in the navigation pane to show the desktop on the start screen and then going there. (to the start screen) (And just to not create a conflict, I did not install Decor8) I think when Stardock will advertise this as a new and stable feature and put videos on the start screen on their website as a sales point, then perhaps ... well ...
Not there yet! Best of Luck.