I've just returned to discover I have hardware problems so I won't be able to test things out for some time.

Here's something you can try:

Find the WireShare.props file in your WireShare settings folder. Find a line that says either HOSTILE_IPS=
or BLACKLISTED ... =

Add the ip addresses you wish to and have a semi-colon after each one except the last one. Make sure there are no spaces.
eg:
HOSTILE_IPS=238.108.1.3;239.4.8.23

Save the document without changing the file format and do not choose any saving approach that creates a Rich Text type of document. Retain the .props file extension. See if that works.