Setting up a remote BOINC client seems to be a bit confusing, mainly due to the lack of error messages. This is what you have to do to get it working.
sudo apt-get install boinc-client/etc/boinc-client/remote_hosts.cfg to add the manager's IP address. Do note that wildcards / CIDR ranges don't seem to work!/etc/default/boinc-client to enable RPC control.
Note that if you want to remove hosts from BOINC Manager's interface, you will have to manually edit ${HOME}/.BOINC Manager.