Do you really need a rear wheel carrier? I wanted one, and now have one but it's a PITA. It used to be so easy to get into the back of the Cruiser, but now I have to unlatch the wheel, swing it away, then open the top section, and closing it again...
It seems small but it is much less convenient.
That said, in answer to your question I would put a jerry can holder on the other side.