In Visual Studio 2010 they added much better support for targeting multiple frameworks, allowing us to target .NET 2.0 and 4.0 from the same solution, which also gives us the ability to target runtime's such as Mono.
Jonathon Pobst has done all the work needed, so download his template from here and you are good to go!
I've also mirrored his template here in case his site goes down. Just extract the file to C:\Program Files\Reference Assemblies\Microsoft\Framework\.NETFramework\v3.5\Profile and tell your project to target mono!