Hi Jesse,
There are several ways to do this... but the one that's built-into the V2 product is to add a "post-deploy" step to the "node template". Using the Admin console, select the node template (perhaps the default one). Find the 'Edit Template' option and you'll see the facility for adding such post-deployment commands.
See examples at http://edge.technet.com/tags/hpc.
Thanks for using Windows HPC Server 2008.
http://channel9.msdn.com/shows/the_hpc_show