Azure Storage Queue - correlate response to request

When a Web Role places a message onto a Storage Queue, how can it poll for a specific, correlated response? I would like the back-end Worker Role to place a message onto a response queue, with the intent being that the caller would pick the response up and go from there.

Our intent is to leverage the Queue in order to offload some heavy processing onto the back-end Worker Roles in order to ensure high performance on the Web Roles. However, we do not wish to respond to the HTTP requests until the back-end Workers are finished and have responded.