xticklabels: how to position majors on top/north, minors on bottom/south?

Hi list,

how can I position major xticklabels on top of my axes an minor xticklabels on bottom?

Example:

Datetimes on xaxis, minors = hours, labels as usual below xaxis, majors = days, labels on top of my axes:

  23.07 24.07 25.07 26.07 27.07 28.07

···

--------------------------------------------------------------

        x
x x x x x
x x x x x
   x x x
                   x
                    x
                      x
                       x
                        x
                         x

---------------------------------------------------------------
   0 6 9 12 18 0 6 9 12 18 ........

Regards
Simon