**Semi-long-winded and embellished trip down memory lane alert**
I have been fortunate enough to own a handful of vintage Guilds with Bisonics and several other basses with pickups inspired by the original Hagstrom design. I first joined the junior rank of Bisonictitions though about ten years ago... I had an Ibanez ASB-140 bass, which was a semi-hollow, single pickup bass and the closest thing to a Starfire I could afford at the time. I was not the biggest fan of the somewhat sterile sounding stock humbucker, so, in accordance with my Casady/Airplane obsession, I had a Hammon Dark Star installed in it. Right off the bat I was slightly disappointed since it did not sound exactly like the bass on Crown of Creation. However, over time, I realized how sensitive the pickup was to the slightest changes, i.e. right-hand position, type of strings, volume/tone controls, etc. My disappointment quickly morphed into excitement and a craving for further exploration into the possibilities of these pickups. All of a sudden I found myself stumbling onto new sounds that were no doubt inspired by and reminiscent of Casady and his Starfire, but chiefly characterized by my own hands and limited amplification options. The pickup taught me quite a bit about how sloppy some of my technique was and enabled me to spear-head the improvement efforts of my bassing. All was relatively well and good for some time. Eventually though, late in the evenings, when all was quiet and the lights were dim, I started noticing my bass and I were not alone. Lurking over my shoulder and breathing down the back of my neck was the ever-loudening ghost of 60-cycle hum and his clattering chains of electro-magnetic interference. Before I knew it, I could no longer play along to my favorite Airplane records without his haunting presence interrupting and sabotaging me at every pluck of the string. I started researching on methods of ousting this monster from my life. I could not afford another Dark Star and the professional installation thereof to bring down the mighty cleansing hammer of a hum-cancelling pair, so I turned to other, more accessible means... namely the giant vat of snake-oil that is the Electro Harmonix "hum-debugger". I was hopeful; could this be the answer? The secret of sonic exorcism I had been looking for? No. After less than an hour of a misled sense of victory, I started to notice that the demon was now simply toying with my heart... he did so by shifting his evil from the space between my notes to the notes themselves! I noticed a strange glitchy, almost digital-sounding, unstable warbly quality to my notes. Perhaps the smoke and mirrors of the Hum-debugger creates enough of an illusion for an overdriven guitar with single coils, but when it came to the lush tones produced by the Bisonic, it did more harm than good. At this point, I simply learned to accept the fact that, if I wanted to wield the sword of a solo('d) Bisonic, the 60-cycle ghost would never leave.
HOWEVER, this is not a sad tale of defeat... as with anything in life, we must accept the good with the bad. Sure you can add another Bisonic to make a hum-cancelling pair, but it when both pickups are engaged, your bass will sound different than it does with a solo('d) Bisonic. Also, there is the possibility of a "dummy coil" (in a sense, a separate, incomplete pickup which also creates the desired hum-cancelling without creating its own signal), but even this will affect the tone of your Bisonic to a certain degree, since it is another complete coil and a whole lot of wire for your signal to travel through.
I think the best solution to this problem, if you truly love the tone of your bass the way it is (aside from the hum) is to just accept its flaws as they are vastly overshadowed by the lush greatness of the Bisonic pickup. That said, it will help to some extent to make sure the pickup cavity is properly shielded with shielding paint or copper shielding tape. This will get rid of some noise, though the 60-cycle single coil hum will remain.