Is it possible from Spring to inject the result of calling a method on a ref bean?

It's possible in Spring 3.0 via Spring Expression Language:

<bean id="registryService" class="foo.MyRegistry">
...properties set etc...
</bean>

<bean id="MyClient" class="foo.MyClient">
  <property name="endPoint" value="#{registryService.getEndPoint('bar')}"/>
</bean>

The nicest solution is to use Spring 3's expression language as described by @ChssPly76, but if you're using an older version of Spring, it's almost as easy:

<bean id="MyClient" class="foo.MyClient">
   <property name="endPoint">
      <bean factory-bean="registryService" factory-method="getEndPoint">
         <constructor-arg value="bar"/>
      </bean>
   </property>
</bean>

Or in Spring 2.x, by using a BeanPostProcessor

Typically, bean post processors are used for checking the validity of bean properties or altering bean properties (what you want to) according to particular criteria.

public class MyClientBeanPostProcessor implements BeanPostProcessor, ApplicationContextAware {

    private ApplicationContext applicationContext;
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if((bean instanceof MyClient)) && (beanName.equals("MyClient"))) {
            Myregistry registryService = (Myregistry) applicationContext.getBean("registryService");

           ((MyClient) bean).setEndPoint(registryService.getEndPoint("bar"));
        }

        return bean;
    }
}

And register your BeanPostProcessor

<bean class="br.com.somthing.MyClientBeanPostProcessor"/>