[gentoo-dev] ebuild optional dependancy question

Hello everyone!

I'm a recent convert to gentoo from debian (at least on my workstation) 
and I love it!

Gentoo doesn't have two of my favorite programs available as .ebuilds.
No big deal, I decided to roll up my sleeves and get cracking on
creating them for everyone.  And herein lies the problem.

The first program (zile -- zile.sourceforge.net) was a breeze using the
skel.ebuild.  I plan on uploading it to bugs as soon as I get my second
ebuild correct.

The second program (yafc -- yafc.sourceforge.net) is not as
straightforward as zile.  For the uninitiated, yafc is an interactive
ftp client similar to lftp with support for socks4/5, kerberos4/5, and
sftp.  Yafc's configure script automatically enables/disables ssh and
readline if it finds the libraries.  The same is not true for socks and
kerberos.  I merged kth-krb (kerberos4) and saw it installed everything in
/usr/athena.  When I manually gave configure the parameter
--with-krb4=/usr/athena it compiled with kerberos4 support.  I had similar
results with dante (socks4/5).  

After discovering I had to manually apply parameters to the configure
script in order for socks/kerberos support I went looking for use
variables. I planned on using the "if [ -z "use_var" ]" trick from the
gentoo-howto.  Unfortunately I didn't see either socks or krb4/5 use
variables.  

So my question is this:  What is the correct gentoo way of discovering
these packages?  Should I consult /var/db/pkg/app_group/app_name* to see
if the program is installed?  Should I check the physical location for
the libraries (a la -d /usr/athena)?  Or am I just a numbskull and
missing some obvious feature of portage which makes my life much easier?

Any help is appreciated -- I'd love to maintain a couple of ebuilds for
everyone.  It sure seems easier being a maintainer for gentoo than for
debian ;).

-- 
Brian M. Rzycki
"Alright, WHO let the polack near the computer?!?"