I guess the problem was solved while I was typing. But here is my answer in case anyone else has the same question:
You have several options to deal with the lack of breaker space.
First, to avoid the possibility of command ping-pong you should not use the XTB-IIR with another repeater. So, simply replace the HCA02 with the XTB-IIR. (The XTB-IIR does have a mode option to break the ping-pong loop if for some reason you want both in the circuit.)
Some panels accept skinny breakers that allow twice as many circuits in the same space. There are also quad breakers that use the space of two standard breakers, but provide two independent 120V circuits and a 240V circuit. That is what I used here.
Or, you can swap two adjacent full size breakers for a 240V breaker, and then add a junction box external to the panel for the XTB-IIR before those two circuits branch off independently. Most kitchens today have at least two circuits, so that is a candidate for running through a shared breaker.
You can certainly run the XTB-IIR off just a single phase, but you would have to install a good passive coupler at the panel to propagate its strong signal over to the opposite phase. So, you would have to replace the HCA02 with something like the X10 XPCP.
Jeff