After some late nights, I've mostly got a template working for Sparrow and Xcode 4:
Unfortunately I haven't solved one part of it: you have to manually update the link and dependency to Sparrow-Framework after creation. The README.txt in the Sparrow folder explains how to do that. It's annoying, and I really want to fix it, but short of having a copy of the project in the template folder (which is more yucky), I can't think how to.
This was mostly hacked together over the course of a few late nights, so no doubt something will break. If you spot any issues, let me know and I'll try and fix them.
The template uses a simple ViewController I knocked up, mostly because I wanted the standard system rotation code to work. It also means there's a RootViewController, so if anything attaches things to it (some analytics frameworks use it to show modal dialogs, or login screens for game APIs), they should work fine.
When you create an app, the main starting point to add stuff is
<game name>ViewController.m in the initDisplayTree method.
Hopefully someone finds this useful, or can create a more useful template from it 🙂