SQL Server Management Studio 2012 separated toolbars
The only option close to what you need is to mark the control as "Begin a Group", to create a separator to the left of the control. 

Open SSMS > Tools > Customize > Commands tab > under Toolbar select "Standard" > highlight "Activity Monitor" > click Modify Selection and you can (un)tick "Begin a group" and see how the toolbar changes. You could edit the Name to start with something like "__" for visual comfort (doesn't seem to take extra spaces).