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...

Seth