The quick answer is yes you can do it (I did it a long time ago). What you'll need to do is completely gut the current fixture and get a new reflector. You will need two more ballasts and two more sets of endcaps. Try to get ones that don't need starters (the cylyindrical thing in your picture). At this point its just wiring and mounting the endcaps. In my experience there was not enough room in the hood for all three ballasts so I affixed them on top (not to pretty, I know). It seems daunting, but almost all ballasts have wiring instructions on their label.
Good Luck
Carl
By the way what size light is that? It looks like a two footer to me, but if I'm wrong I have some extra ballasts for 36" flourescents tha I'd be willing to part with them cheap.
Carl