We have been developing a middleware suite called GridARS that enables co-allocation of computing and network resources from multiple administration sites. In such middleware, it is important to provide each user application with a slice which is a set of dynamically allocated resources distributed across sites. However, there are the following issues in constructing such a slice automatically: 1) multi-site administration heterogeneity, 2) dynamic determination of application configuration information, 3) distributed resource monitoring, and 4) asymmetric network reachability. We design and implement an application execution system that provides each application with a slice, that mimics a conventional computing cluster system over the dynamically allocated resources. From the demonstration of the proposed system on an emulated wide area network environment, we confirmed that: first, the proposed system can fully automate resource allocation, slice construction, application invocation, and resource monitoring, in coordination with GridARS. Second, the proposed system can setup a slice quickly, even if the allocated resources are widely distributed and their communication latencies are high. This is because the overhead for gathering and distributing contextualization information is small, and OS-level virtualization and stackable file system technologies accelerate the contextualization process at each node.