Thanks Christian
I knew there had to be a config (or rather, template) file somewhere to achieve this end. Having opened /usr/share/zentyal/stubs/dhcp/dhcpd.conf.mas however, I find a bewildering array of text and nothing to suggest what I need to add/edit to advertise option 60 in my DHCP responses.
# extra options - seems like a likely place to write the option, but how is one supposed to know the syntax? It could be anything, really.
Regards
xdd