put a uicontrol('style','text') inside a uipanel and keep resizing it to be large enough to hold all current text. Create a scroll bar that adjusts the Position of the uicontrol within the uipanel.
It can be easier to work things out properly by having a uipanel 'B' inside a uipanel 'A', with the scroll bar in 'A' adjusting the Position of 'B' relative to 'A', with the uicontrol('style','text') inside B.
You might also want to look at http://www.mathworks.com/matlabcentral/fileexchange/29776-scrollpanel