raschemmel:
After thinking about it on the way to work , I realized that even if you only had one of each type you could still do it by putting the stepup first and step the voltage up to 6V, then use the stepdown to step it down to 3.3V.
That's one way to make a buck-boost. That way makes it easy to visualize the efficiency hit too.
The LTC3335 explains how its buck-boost works on page 14 of its datasheet.