I still can't see any reason to compile in Release, Unity doesn't use any of the files compiled from Monodevelop. The project file that Unity generates when you double click / select "Open C# project isn't set up for building in release, none of the defines are set.
If you really want to compile in release for some reason, you will have to fix the project file by hand, eg. right click Assembly-CSharp, Options, and copy some of the settings from debug to release. You'll have to check on the unity forums for what exactly to copy, but you can trial an error your way around it, its not too complicated.