So the ideal situation would be to add the jsp to the application after it has been deployed. I could have the system administrators add the file to the WebSphere installedApps directory, but this isn't recommended (and they would likely not agree to do this anyways).
A proper alternative is to use WebSphere's deployment process. Instead of updating an application using the default option, look further below on the page:
The contents of the zip should mirror the exploded folder structure in installedApps. In this case the zip contains a single JSP: