always Connect to a virtual display

Hello guys

i have a mountain lion server and i have two user on it. (User A and User B)

when i want to connect to the mac using user "B" If user "A" is already connected to the Mac, a dialog asks if i want to share the display with the other remote user (“Share the display”), or set up your own screen (“Connect to a virtual display”).

i don't want to see this dialog i want user "B" always connect to a virtual display. i want to disable the permition to share the "A" user.

i will be happy if someone can help me!

thanks 😉