A Visual Studio addin: right-click on method, choose "run in LinqPad"
From VS, right-click on selected method, choose "Run in LinqPad". It creates a new query, copies the method from the source, adds using statements from the top of the file, and reference dlls used by the project. Likely would also need a way to reference other code files within the same project and/or reference the current dll
Rob shared this idea