well, no, two items cannot have the focus.
But, what you can do is tell the osk what should have the focus when it is clicked. To do this, you can get the handle of the window that you want to send the keyboard input to, and then use a PostMessage of SendMessage
check out the forum here:
Virtual Keyboard- C#[
^]
There are a couple of solutions. There is also a zip file called BensOSK towards the bottom thirds that is interesting.