Yesterday when I checked the Syrah I found that the malolactic ferment was producing enough gas to bring the cap back up. I gave the must a mix (#14) and then shot some nitrogen into the headspace using two of the gas cartridges supplied with the Pod.
These cartridges each supply 1.8 g of N2. Dredging up some freshman general chemistry from memory, this comes to about 1.44 liters of gas (at STP) per cartridge.
I have not made an exact measurement but I'm guessing the headspace is more like 4-5 gallons, meaning it would take about 12 cartridges to purge this volume with nitrogen.
If the cap falls again before the tannins have softened I will probably fit the variable-capacity lid to the Pod.