[gentoo-user] How to thin package.provided ?

Hi,

I want to mark some software as provided from other sources.
And want to prevent long comments from emerge and friends about
my doing so.

/etc/portage/profile/package.provided seems to be a good place for
that...but according to the documents, one needs to specifiy a version
and relational operators are not allowed...which make me think that
I have to mention any single version in past, current and future
existence to prevent emerge from installing a previous or current
version of that software for a longer time.

Thinking of some packages, which are getting updates very often I 
see myself writing scripts to populate package.provided with a 
lot of stuff and scripts to delete obsoleted entries from there.

If I put those packages into package.mask, emerge comments on
every update of the system, that "needed packages are masked".

Is there any clean way to get out of this?

Cheers
Meino