While practicing today I wanted to play a couple of notes about a 5th beyond the end of my fingerboard, arco. The tone almost started to work, but not quite. I've played a semi-tone beyond fairly frequently and found that as long as my thumb was solidly on the fingerboard, I could get an acceptable tone. I experimented for 10 minutes or so - heavier bow, lighter bow, faster, slowly, nearly right on top of the bridge but, it all sounded bad to me. Is this doable with good technique or just a fool's errand? If so, what's the proper technique, light, slow bow as close to the bridge as I can get?