Segregating Debug and Release Code in C#

I'm writing an application wherein I have some debug code that I do not wish to delete, but I wish it to be modified or removed when compiling for release/publish. For example, I would like something like this in a debug build:

MessageBox.Show(ex.ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

...to become this in a release build:

MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

Ideally, I was hoping to do something like this:

#if DEBUG_BUILD
   MessageBox.Show(ex.ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
#else
   MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
#endif

I would prefer to not have to add/remove a Conditional Compilation Symbol in the project properties every time I change the build type; it should happen automatically. Is there a way to do this in Microsoft Visual C# 2008 Express Edition? Thanks.