Unless Russia makes its own peace deal and demands a couple of the provinces it occupies (which can be done by reloading as Russia, placing the demand, and saving without restarting the clock, then reloading again as your previous country), the only option would be for you as war leader to demand provinces from Austria that are occupied by Russia. YOU would sufferer the infamy hit for them, not Russia, and Russia would get the provinces. There's probably not enough potential war score (only goes to 100) to take more than around 2-4 provinces in one war, regardless of who takes them.