[oe] task-base extra stuff

[Nicolas FR]

After reading HRW's interesting article:
http://www.hrw.one.pl/2006/12/12/how-to-use-task-base/
I have a question: I made an image for x86 target and used task base.
I understand how to add extra stuff with
MACHINE_EXTRA_RDEPENDS/MACHINE_EXTRA_RRECOMMENDS but is it possible to
do the reverse:

I do not want to pull psplash even if my machine features "screen". Is
it possible? (I tried ASSUME_PROVIDED += psplash in local.conf but
psplash is always added to the rootfs image).

Nicolas.