allow wall post to non-logged in users

My client bought the activity extension and I added the wall to the user profile on their site. Now he tells me, that a user need to be logged in to be able to post something on a wall.

Is it possible to set it up, so that a regular visitor can leave a post on the wall?

I’m using the shortcode like this:

[ultimatemember_activity user_id=”123″ user_wall=1]