The best solution to this would be to place "prepareit.do" in the web.xml welcome file list.
Unfortunately, I can't do this, because I use WebSphere as my Application Server, and WebSphere only supports URIs in the welcome file list that are backed by physical files such as index.html, or index.jsp. It does not support virtual URIs such as "prepareit.do" that are only resolved at run-time.
I've been told that WebLogic does support virtual URIs in the welcome file list, but I haven't verified that first-hand.
All I can tell you is that if you use an Application Server other than WebSphere, try putting "prepareit.do" in the welcome file list. If it doesn't work I'm afraid you're stuck with redirecting from an index.jsp page.