Unicast is a one-to one connection between the client and the server. Here it is not possible to detect other (unknown) server exept you scan a list of IP addresses.
It will be a bigger effort to configure it.
Anyway, I do not know any configuration how to change to unicast.
I suppose it is not implemented.
Why not just switch all nodes to use a tcp-based jgroups stack? e.g.
./bin/run.sh -c all -Djboss.default.jgroups.stack=tcp
Since multicast is not an option, you'll need to manually edit the jgroups configuration and replace MPING with TCPPING and define the cluster members statically. The relevant file is: $JBOSS_HOME/server/all/deploy/cluster/jgroups-channelfactory.sar/META-INF/jgroups-channelfactory-stacks.xml