GT 4 Pro Piano Roll View: Volume Swell / Decrease of Single Midi Notes?

Hi all, I am trying to make my orchestral instruments as realistic as possible by adding volume swells and decreases to individual notes: it might start soft and get louder, and vice versa. Using the control pane at the bottom of the screen, I can draw volume changes with the Draw tool, but it only seems to work for measures rather than individual notes. Am I doing something wrong? Is this even possible with GT4 Pro?
 
Many thanks.