Change windows layer order via command line

Hi there,

I'm trying to change windows'layer order via command line in fluxbox.
I tried wmctrl but it only allows to change the _NET_WM_STATE property
that means I can just switch between "above" and "below" property.
Fluxbox instead is able to manage up to 6 different layers (Desktop,
Bottom, Normal, Top, Docks and Above Docks) and I'd really like to be
able to specify a particular layer for each window by typing a command

wmctrl -win_id 0x123456 -win_layer desktop

or whatever.

Any suggestion?
Thanks in advance,