Basically you just need to edit the version number embedded in the project file. I've posted the full step-by-step details to my blog.
Here are the steps:
- Right-click a project and select 'Show Package Contents.'
- Find the projectData file and open it with the Plist Editor (or a text editor if you don't have the Developer Tools installed).
- Find the version key with the value 45000 and change that to 40000.
- Save the file.
[crarko adds: I haven't tested this one. Hopefully Apple will have that update out soon.]

