Then that's about the best you can do. While it may not be as effective, it should still be an improvement. We make sacrifices all the time. Sometimes with speaker placement, sometimes by just not having an ideal room. We can bend the laws of physics, but we can't break them. The last room I had was filled with crown molding too. While the Triangles weren't as effective, there were still a major improvement. Do what you can and be happy with the compromises you have to make. It's about the music after all.