I wrote a theme that does what you want, i think. I tried ton the Clip + and Clip Zip.
Menus, brouser, context, and playlist still works. I use it for poker tournaments.
Blackout.wps
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# Disable default status bar
%wd
#Disable Backdrop
%X(d)
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If you make the battery to last, turn off the EQ
Blackout.cfg
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wps: /.rockbox/wps/blackout.wps
font: /.rockbox/fonts/15-ProFont.fnt
eq enabled: off
foreground color: ffffff
background color: 000000
volume display: graphic
battery display: graphic
selector type: bar (inverse)
statusbar: bottom
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