The IBC puts out 600mA per bay. For a 750mAh cell this means a charging rate of 0.8C, which is fine. The AW R123 is the best on the market. His dummy cells make good spacers as you suggest.
As the cell gets older (way off in the future!) it will lose some capacity and you will need to supervise charging carefully, as there will be a danger than it could overheat. 1C is the safe limit for charging Li-Ions.