I am not aware of any officially supported means to extract the partitions from a Zynq Boot Image file.
However, if you take a look at Chapter 6.3.2 in Xilinx UG821 there is a more detailed description of the format used for a boot header used in the image file:
So with an understanding of how the file is structured, theoretically someone could extract the individual partition components from the BOOT.BIN container file.
