How do I configure hibernate ORM on heroku?

You can use this Hibernate+JPA persistence.xml configuration as a base for your hibernate configuration.

The property names between the hibernate.cfg.xml and the persistence.xml are the same, only hibernate uses opening and closing elements whereas JPA uses attributes.

<properties>
            <property name="hibernate.connection.url" value="jdbc:postgresql://ec2-107-21-126-162.compute-1.amazonaws.com:6232/dbname?username=username&amp;password=password&amp;ssl=true&amp;sslfactory=org.postgresql.ssl.NonValidatingFactory"/>
            <property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
            <property name="hibernate.connection.username" value="username"/>
            <property name="hibernate.connection.password" value="password"/>
            <property name="hibernate.archive.autodetection" value="class"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hbm2ddl.auto" value="update"/>

            <!-- c3p0 connection pool settings -->
            <property name="hibernate.connection.provider_class" value="org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider" />
            <property name="hibernate.c3p0.min_size" value="1" />
            <property name="hibernate.c3p0.max_size" value="5" />
            <property name="hibernate.c3p0.acquire_increment" value="1" />
            <property name="hibernate.c3p0.idle_test_period" value="3000" />
            <property name="hibernate.c3p0.max_statements" value="50" />
            <property name="hibernate.c3p0.timeout" value="1800" />

        </properties>

Maven dependancies:

 <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>4.2.1.Final</version>
        </dependency>       

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-c3p0</artifactId>
            <version>4.2.1.Final</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>4.2.1.Final</version>
        </dependency>