Brian - no doubt you know this but just to complete the picture for others who may read this later, you can put a dummy 123 cell in-line with a RCR123 and other 35mm long cells. This is how you charge a single RCR123 / 16340 / 18350 cell in a Pila charger. AW and other cell suppliers offer these pass through dummy cells.
The spacers included with the Pila allow for an 18500 cell to be charged in each channel.
Here's mine with an IMR16340 + Dummy CR123 in one channel, and an 18500 + Pila spacer in the other.
You don't have to buy dummy 123 cells -- the two Pila spacers stacked together will allow 123 sized cells to be charged but you'd only be able to do one cell at a time then. A pair of dummy cells doesn't cost much and may be useful in some lights as well.