Jenn-Air cartridge retro-fit 3 prong/4 prong

Older Jenn-air cooktops swappable cartridges used 4 flat blade power prongs plus round pin - each burner or grill element had its own feed from controller and return.

Newer cartridge set-ups use three prong (plus round pin) … presumably the two elements share a common neutral.

Older four prong cartridges are no longer avail.

I want to purch. a three prong two-burner cartridge to use when not grilling/griddling but needing four burners total.

Which is easier and where can I purch conversion parts:

  1. Add fourth prong to cartridge plug (which would just short between rightmost and neighboring prong)

2 re-wire existing outlet (or re-wire at controllers?)

Does anyone have any info on a mfr. "retro kit" which presumably would have been made avail when they changed wiring config?

Thanks
Mark