Compiling to different directories

Gnatmake has the "-i" switch to direct that the object and ALI files for a
compiled source file be placed in the source file's directory, rather than the
current directory.

I have been unable to identify a way to do this using GPS Project configuration.
 Everything gets compiled into the build directory that I specified for the
project (which, admittedly, is doing what I say, but it isn't what I _mean_ :-).

It appears I would need a separate project file for each directory that would
then be imported into my project.  But that isn't really what I want, since some
of those directories are simply collections of utilities or common code, and
there is no "project" per se in them.

How can I get the "-i" behavior?

I'm using GPS 3.0.0 from the GNAT GPL 2005 distribution.

-- Marc A. Criley
-- McKae Technologies
-- DTraq - XPath In Ada - XML EZ Out