readconnroute router restrict reads to slave(s) only

Maxscale with router=readconnroute to allow read traffic to be served even when the replication is broken (i.e slave IO or SQL process stopped). As per documentation we can do this by setting the router_options=running. However, with this setting this also sends traffic to the Master DB which we do not want. We want the read traffic to only go to the slaves even if the replication is broken. Master DB should only be chosen as a read candidate if none of the slave servers are available.
It seems like it's not possible to configure readconnroute to use all other servers except the master.