Currently it is not possible, because the GUI of the UCCNC is not Windows GDI+ graphics, it is not even Windows Forms graphics, but an OpenGL 3D screen. The buttons are bitmap images rendered on triangles.
So, there are no events for tooltip, because the GUI is all drawn with code and they are not buttons in real.
We could ofcourse implement tooltips with code and could make it act like if it was standard Windows tooptips, but we did not think that it would be useful for anything, so we did not implement it yet.