Going back to VS 2003 for a month and doing all the same stuff you do today (but more productively in VS 2010) as a test.
I feel your pain. Had to maintain an ASP.NET 1.1 web application for ages, and that got me back to VS 2003 over and over. They should include that as a valid cause for medical use of controlled substances.
@ZippyV: actually, there's an easier way: VS2012 can use VS2010 solutions without upgrading. One can always create the solution in VS2010 (on a machine not tainted with .NET 4.5), then develop with VS2012 targeting .NET 4. In the remote case where you get a bug during testing that doesn't repro in VS2012, it's always possible to go back to the VS2010 machine and debug away.