piggybacking on Mac's idea of recording the bass with Midi guitar, then dropping an octave...
even if you don't have a MIDI guitar, you can record bass on the guitar as audio, then use Audacity to lower the pitch an octave without changing the timing. I doubt it would sound like an acoustic upright, but it approximates an electric bass fairly well.
You might experiment with an acoustic guitar, classical guitar, electric guitar etc to see which lowered sound is closest to that of a natural bass