@Bean
    BeanPostProcessor delegateForFoo() {
        return new WrappingBeanPostProcessor<>(Foo.class, original -> new MyCustomFoo(original));
    }

    public class WrappingBeanPostProcessor<T> implements BeanPostProcessor {

        private final Class<T> type;
        private final UnaryOperator<T> beanCreator;

        private WrappingBeanPostProcessor(Class<T> type, UnaryOperator<T> beanCreator) {
            this.type = type;
            this.beanCreator = beanCreator;
        }

        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

            if (type.isInstance(bean)) {
                return beanCreator.apply((T) bean);
            }
            return bean;
        }
    }