portdowngrade and portmaster

I grabbed some old version of a port with portdowngrade and renamed the folder. Now I want to install it with portmaster because I want to create packages.
I don't want to copy the folder to the port tree or create a symlink.
Is there any other way to tell portmaster to install the port that's sitting outside the port tree?
make -DBATCH package, make missing, make run-depends-list, make build-depends-list, make all-depends-list

See ports(7).