How does a pilot maintain stability for an unbalance loaded airplane?
Use the available trim (elevator, and rudder if installed), and then manage the left/right fuel tanks if they are not feeding evenly.  Use the autopilot if so equipped, even if it's just a single axis wing leveler. 

With just 1 passenger, it is hardly out of balance tho. The POH has a Weight &amp; Balance chart as seen here  How are the limits of the center of gravity chart established?, plotting front seat weight and fuel will show the plane to be well within limits.