:sort vimoutliner file on header

[striker]

I have a Vimoutliner file for a soccer team that contains names in  
the headers.  File example below:

[X] 100% Soccer team
        [X] 100% Sims, Tim
                [X] 100% physical
                [X] 100% uniform deposit #31

        [  ] 50% Smith, Sam
                [  ] 0% physical
                [X] 100% uniform deposit

        [  ] 0% Comer, Hannah
                [  ] 0% physical
                [  ] 0% uniform deposit #8

        [X] 100% Thornton, Tyler
                [X] 100% physical
                [X] 100% uniform deposit #35

I would like to sort the names and keep the lines below each header  
with the appropriate header.
I did try folding and then sorting, but the fold was ignored and all  
lines were sorted.

Any suggestions?
TIA,
Kevin