how to use my local CPAN mirror?

[Mark E. Perkins]

I maintain my own mirror of the CPAN.  That way I have ready access to
whatever uninstalled Perl modules I might need when I am off-net.  I don't
see a knob in MacPorts that allows me to point at my archive when I want to
install p5-foo.

I can always use the cpan command for those, but I'd rather let MacPorts
keep track of everything for me.

Did I just miss something?  Or is this not possible?

Thanks,
Mark