Thanks demerphq and PodMaster; this is at least getting me close. There is some magic here. My directory structure looks like this:
in reply to Re: Re: MakeMaker to make Makefile in subdir
in thread MakeMaker to make Makefile in subdir
All I had to do was put a simple Makefile.PL in the src/ directory and when the main Makefile.PL was executed in the gmod/ directory, it saw the one in src/, which in turn saw the ones in component directories.
This probably would have worked flawlessly if the items in the component directories were only Perl modules, but they are more complicated than that, and have in their Makefile.PLs custom overrides to the install target (so that items can be installed under /usr/local/apache, for instance). I may be able to get around that by overriding the install target in the main Makefile.PL, but that is unattractive for at least one reason: it makes the main Makefile.PL more fragile (if the author of component1 changes his Makefile.PL and doesn't tell me, it won't work as expected).
Project coordinator of the Generic Model Organism Database Project