Can you post your config so I can build a plugin for it?
However, the udp-broadcast-relay-redux tool allows arbitrary relaying of UDP packets between interfaces, and this helps to solve the problem.
I've re-compiled it with a more sensible name and fixed the rc.d file which was badly formatted and Opnsense hated.I'll re-post the archive tomorrow with full instructions on how and where to install the required bits and how to keep it ticking over using Monit.