Given the high proportion of HTTP traffic in the Internet, Web caches are crucial to reduce user access time, network latency, and bandwidth consumption. Prefetching in a Web cache can further enhance these benefits. For the best performance, however, the prefetching policy must match user and Web application characteristics. Thus, new prefetching policies must be loaded dynamically as needs change.Most Web caches are large C programs, and thus adding one or more prefetching policies to an existing Web cache is a daunting task. The main problem is that prefetching concerns crosscut the cache structure. Aspect-oriented programming is a natural technique to address this issue. Nevertheless, existing approaches either do not provide dynamic weaving, incur a high overhead for invocation of dynamically loaded code, or do not target C applications. In this paper we present µ-Dyner, which addresses these issues. In particular, µ-Dyner provides a low overhead for aspect invocation, that meets the performance needs of Web caches.