How to enable the Federated/FederatedX storage engine on MariaDB 5.5?

Question

I upgraded from MySQL 5.1 to MariaDB 5.3 and then to 5.5 on a Windows machine. Everything works well, except I can't enable the federated storage engine. With MySQL 5.1 and MariaDB 5.3, I just added "federated" under [mysqld]. If I try to start MariaDB 5.5 with the same "federated" option, I get an error:

C:\Program Files\MariaDB 5.5\bin\mysqld.exe: unknown option '--federated'

How can I enable the federated storage engine?