I find myself useing my left hand thumb to reach interavals that aren't in my normal range. I will elevate the neck of my bass to get my left hand on the front side of the neck, anchor my LH thumb in the lowest fret needed and then I will usually use my index and middle fingers to reach further up the neck. I don't usually use this technique except when I'm on my G-string. I saw this while watching the BETJAZZ channel. It was used on a Double bass but I seem to have worked it into my functional arsenal. Just wondering if other players have used this technique? It took a little practice. And I think it is a little showy. Is showy even a word. Ah hell, you know what I mean.