It seems I might have to go with the transformer method with a split transformer to produce all output voltages because
I don't understand this app note:
C:\Documents and Settings\Dan Nguyen\Desktop\AN-1082.pdf
about synchronizing a boost converter's clock to the output of a buck converter, but it also mentions that the input to the buck converter has to be in continuous mode and that the input voltage shouldn't vary by more than 10%- something which I can't guarantee.