Monodevelop won't comipile due to "default parameters" not supported?

Recently started using the Loom threading framework which uses default parameters and I can no longer compile from Monodevelop due to the following error.

Default parameter specifiers are not permitted (C50241)

I’m aware this problem has been reported here: Default Parameter Specifiers Are Not Permitted - Unity Answers

However no good solution is given. The suggested solution is to switch monodevelop to .NET 4.0 however this change does not save and must be done each time unity is opened.

Is there a solution that does not require me to refactor a hundred different functions or to keep having to set my target framework to .NET 4.0?

My solution to this was to switch to the Visual Studio IDE with the UnityVS plugin for debugging. It seems to preserve the .NET version number between sessions.