Is there a way to manually resize the controls inside an editor window at runtime?

As far as I know, we have 2 way to control the layout of multiple controls inside an editor gui : - using the EditorGUI and GUI objects, wich we pass rectangles to them in, - using the EditorGUILayout and GUILayout objects, wich use an automatic layouting system.

But it both cases, each controls have a fixed proportions. If I resize the entire window, the controls keep the same proportion, and with rectangles, they keep the same size whatsoever.

So, is there a way to resize ourself the controls when using the editor?

To illustrate, I have this :

 public void OnGUI
 {
     EditorGUILayout.BeginHorizontal();
         GUILayout.Button("hello");
         GUILayout.Button("there!");
     EditorGUILayout.EndHorizontal();
 }

In this case, how could I "move" the space between the two button with my mouse?

For those familiar with Qt, it is like I'm asking for the features of a QSplitter. http://harmattan-dev.nokia.com/docs/library/html/qt4/qsplitter.html#details