Well, guess I was half right. From pg. 102 of your owners manual:
“■Notice about fuel
●For plug-in hybrid vehicles, fuel may remain in the tank for a long time and undergo changes in quality depending on the how the vehicle is used. Refuel at least 5.3 gal. (20 L, 4.4 Imp.gal.) of fuel every 12 months (refuel
a total of at least 5.3 gal. [20 L, 4.4 Imp.gal.] over a 12-month period), as this may affect components of the fuel system or the gasoline engine.
●If the vehicle has not been refueled for a certain amount of time and it is possible that the quality of the fuel remaining in the tank has changed, “No new fuel has been added recently. Please refuel” is displayed on the multiinformation display when the power switch is turned to ON mode. If the
message is displayed, refuel the vehicle immediately.”
So I’d be using Stabil, unless I was running through at least a tank every 6 months.