A first glance, it seems to be easy : just edit /etc/mk.conf, and put
your MASTER_SITE_WHATEVER=ftp://ftp.localserver.localdomain

At a second, there's a pain : one have to deal with $DIST_SUBDIR, or
'LOCAL_PORTS' added, apparently randomly to your local ftp path.

I read /usr/pkgsrc/mk/bsd.pkg.mk, /etc/mk.conf, a few Makefiles, to no
avail.

Here, at home, I have an (expensive) ISDN connection, so I fetch daily
sups from work on a Zip, and disfiles as needed, but even when present,
the $DIST_SUBDIR problem makes my box connect to GNU's site or
columbia.edu or what else...

Any clue ?

Thanks,

-- 
Xavier HUMBERT  -  Systemes et Reseaux     |     labo-info@injep.fr
INJEP                                      |     humbert@injep.fr