Mike,

 

You will have to do the calculations for an ES and let us know the results. Consider an arbitrary aircraft that carries 25 gallons of fuel in each wing and that the fuel is located between BL50 and BL100 (50 to 100 inches from the centerline) and that the tank is of a constant  shape.  Then BL75 is the fuel tank CG and

 

(75 inches x 25 gal x 6 lbs/gal) / 12 inches/foot = 937.5 as a lateral moment.

 

Assuming the cabin width is 48", let's say a front seat person's CG is at BL18 or 1.5 feet

 

937.5/1.5 = 625 pounds (moment / arm = weight). 

 

If you can find a 625# person to sit on the empty wing side, you would be in balance as though the wing were full (although you may be over gross).

 

A 220# person would be the equivalent of only about 9 gallons evenly spread thru the tank.

 

Think about the wing taper and movement of the CG as the fuel is used - that is, remaining fuel weight is more towards the center of the aircraft and less of an imbalance.

 

The imbalance will be less as you approach your destination.