After some testing I have found a better way to have indirect light in a room. The idea is more or less the same as yours, but I placed the lights above the false ceiling, so that you can't see them from the room. It's not perfect, but maybe you can experiment a bit more to get better results.
Here is the file: http://www.mediafire.com/download.php?mze9jddn7k1n9c6
Hans