Neptune's "Chamomile tea" timeout area ... in search for effective and simple solutions. Please note that my new technology focused blog is at http://blogs.msdn.com/willy-peter_schaub
In the previous build post TFS Build "Workspace already mapped" Issue we covered a common build anomaly and pointed you to Buck's http://blogs.msdn.com/buckh/archive/2007/08/14/tfs-2008-a-basic-guide-to-team-build-2008.aspx post, which is an essential read and contains a reference to an interactive UI build agent.
If you would like to use a "kind of hacky way (and extremely unsupported)", as Ed said, option to host multiple build agents on one server, you can refer to another great blog post http://blogs.msdn.com/jpricket/archive/2007/08/03/tfs-2008-running-two-build-agents-on-the-same-machine.aspx. Following these instructions you can have multiple agents on each of the build server, one being the interactive agent on port 9192
Neno Loje got busy with his blog: Team Foundation Proxy - Your friend for distributed development...