portmaster: upgrade using local packages?

[Angelo Turetta]

I'm evaluating portmaster: I cannot find an option to use pre-built 
packages for upgrading.

My usage-pattern for ports is to build the packages I need (eventually 
with the non-default options I use) on a dev machine (plenty of 
CPU/memory), and then to deploy the upgrades via "portupgrade -P" on 
production servers where the downtime of the services must be as short 
as possible. Always rebuilding from source is sub-optimal in this case, 
also because of the total time for upgrading multiple times the same ports.

I started using portmaster -g on the build machine, but what could I use 
for binary upgrades on the production servers?

Thanks,
Angelo Turetta
Modena - Italy