Model S is a bigger car with bigger frontal area than Roadster. This is a major factor in wind resistance. A car with 10sqft frontal area having 0.4 (very high) drag coeficient has lower overall drag than a car with 20sqft frontal area and 0.25 (very low) drag coeficient. Aerodynamics has its limitations.
It is also heavier (I'd guess around 4000 pounds) meaning it's tyres will have higer rolling resistance (25%?). Acceleration will eat up more energy than it does with the Roadster.
There is one upside though. Model S doesn't need to go as fast. If it was limited to say 105 mph, the motor would have higher average rpm and thus higher average efficiency.
There are still many oportunities to decrease ancillary loads like that little water pump, 100W headlights, combining heater with ESS cooler, etc but all this together cannot improve EPA range by more than 10%.
Model S will need to have higher capacity ESS just to match roadster's EPA range.
This should be doable by using somewhat higher capacity cells. No need to go for top of the line, 2Ah to 2,5Ah (52kWh to 65kWh) is already a 25% improvment that might be enough for 250 miles EPA range.