Clipping Mask to do a 2D GUI list box

Hello, I am doing a menu system for my game right now. I would like to know what is the best way to do a clipping mask for a list box in OpenGL. The list can be of any lenght but the control itself has a set height. Which means that everything too long gets clipped and I show a vertical scroll bar on the side. As the user scroll down, my idea is to simple move up my list which is clipped to the border of the listbox. I would do the same horizontally if some strings in the list are too long for the width.

How can I do that?

Have a look a Gwen gui source - it does a nice job with glScissor for clipping