Hi Deane! If you're willing to record your chord progression *in advance* (as opposed to on the fly) there are various ways of triggering it in sync with the style, leaving both hands free for several measures.

One possibility: You could record a series of triads into a multipad track, with the "chord match" feature DISABLED. Then connect a cable between the keyboard's own MIDI Out and MIDI In. Set up a registration or user program such that the incoming MIDI notes drive the arranger. When you need your left hand, select that registration and trigger the multipad to start the stored progression. I've tested this on a Yamaha and it works! (In the '90s, multipads meant something different than they do today. The PSR-8000 used to have this as a native feature, that's where I got the idea!)

The same technique would work if you stored the triads on a laptop, as a "song" on another KB, or any external sequencer. The trick is synching the MIDI clocks and setting up the arranger to accept chord input via MIDI. By the way, this is also a great way to audition styles with your favorite chord progressions!

One more thought... some Ketrons have a fourth variation or fill which they called a "riff mode." It plays a preset chord progression to jam along to, but I'm not sure if it's editable.
Good luck, you're a great contributor here and I'm sure you'll let us know what you find out!