I liked the suggestion to play an upright because that is the best and only way to get the upright sound. There are some other things you can try and I suspect they have all been suggested by now but I will second (or nth) them by listing them again: an electric upright bass, a Kala U-bass, and a Godin A4. An EUB will generally do a fair DB impression. I have heard clips of the Kala and Godin that sound fairly close too so they are capable if it with the right EQ and what not. Personally I use the poor man's approach: Jazz bass, flats, bridge pickup soloed, foam mute under the strings near the bridge, pluck the notes near the 12th fret. This is far, far from perfect and it will fool no one but it does sound a bit more like a DB than a Jazz bass normally does and you cannot beat the price! Assuming you already own a Jazz or Jazz-like bass....