What I have done as a quick cheat as a 5er cheat, is use my Digitech Bass Whammy pedal. Drops everything down a second or a fourth, so E string goes down to D or B. Works reasonably well. I have the first gen that I have had for at least 15 years. Has harmony and detune setting which is a great chorus sound. Very versatile pedal.
But more notes available at the same time....