Code:
portmaster -d -B -P -i /var/db/pkg/port... /var/db/pkg/port... /var/db/pkg/port...
should solve that problem, but only seventy percent of the time (unforseen dependencies later, only sometimes, still a worthwhile almost-solution if you answer "Y" to the list it shows after about a half-minute or so).
Code:
pkg_version -voL "=" | tee -a /usr/ports/UPGRADE.fil
should show a list to feed to the first portmaster command, maybe a few large ports one night, all the small ones the next (excluding if they were upgraded in the previous one...)