Pending availability of the requested feature,
I can offer a workaround....
Add the first host block rule,
Download the config,
open the file in emacs,
use emacs macro to build the rules
for N hosts, and paste it in.
Upload the config.
(note, brief downtime is required)
I use this technique to add virtual hosts
to our Veritas Cluster at work...the gui
doesn't have "duplicate resource"...
However, in VCS, the application stays
up while the cluster drivers reboot...