Emacs ebuild and LEIM

Hello, 

I am planning on doing an ebuild for the Libraries of 
Emacs Input Methods, or LEIM. The way these are usually
built from source is:

1) the emacs src tarball is downloaded and extracted,
2) the matching (same version) leim tarball is downloaded 
   and extracted into the same dir (creating a new src subdir),
3) emacs is built and installed as normal.

It would be nice if the leim ebuild could be written in 
such a way as to depend on the emacs ebuild, in which
case all the leim ebuild would need to specify is where
to get the leim src tarball. Everything else is already
done in the emacs ebuild.

My question: is there a way to do this? Or does there
need to be a new emacs-leim ebuild that conflicts with,
and mostly replicates, the emacs ebuild?

Or is this something that could be added to the emacs 
ebuild, possibly governed by a new USE variable (say
"multi-byte" for apps that have compile-time options
for multi-byte charset support)?

Please let me know your thoughts.

Ryan