This is a "shoot-from-the-hip" response with the sole intent of opening a possible approach, so ...

I recall having had to dink around with STDOUT/STDERR in a unit test once to keep STDERR from polluting the screen. Perhaps you could set the __WARN__ (?) handler and capture the output to a string where you could then massage it as needed. As I said above, this is just a thought without having had enough Scotch beforehand.