Thinking about this as at work I’m masking nearly 80 piecs a day like this…
First I outline mask a section… then have to manually paint in the interior mask.
Is there a bucketfill command? To auto fill the interior of the masked frame?
Agreed a better solution needs to be added to Zbrush.
You can use Zapplink and stencils to get the same general idea though. Gives you all the selection editing tools inside of PS as well when you do this, so you can use complex paths and such.
http://docs.pixologic.com/user-guide/zbrush-plugins/zapplink/