The simplest way I have ever found to reverse one servo in the tail is to use two different brands of servo with roughly the same specs. For instance, Futaba and Hitec servos spin in opposite directions with the same input, and will do exactly what you want. Since you said yourself that you are only going to be putting around the sky with this airplane, you won't even detect the difference in total throw or speed of two different brands. Bringing linkages from different sides of the servos will produce much greater differences in throw and speed than two different brands will. I have done this in both dual elevator and flap applications to keep the control rods on the same side of the servo(s), more because it looks better that way than anything else.