Close, but it's not a Varitone switch. Varitone switches select between different capacitors to create a notch filter, while the JC bass has an output transformer that selects between three different output impedances.The simplest solution would be to install a JCB-1 humbucker with VariTone control at the same location on another 34" scale bass of your choice. Unfortunately, I don't see that that electronics setup available as an after-market package, so you may need to find a donor instrument. You may want to reach out to Epiphone directly.
Personally, I would do this, though. I love the sound of the JCB but I hate the ergonomics of the semi-hollow, and the Chinese versions I have been able to play in store don't hold a candle to the (rising in value) Korean ones. I'd rather just slap the electronics package in a solid body and be done with it, because it's really that aspect of the sound that I'm interested in.