Looks like this post on RPGWatch an...e to boot DKS Steam version w/out Steam.
The Steam shortcut created is a URL based one which will start Steam before launching DKS. However if you go into the installed folder and into "bin" you will see the standard .exe file to launch the game. Just tested this and it will not launch Steam first.
I tried DKS Demo from Steam - and yep, that trick works.
So, I ran from "bin" folder Divinity2.exe - worked!
I made a shortcut from that and tossed it onto desktop.