There are two ways you can handle this problem. If you have a computer radio you can plug the servos in to seperate channels and mix one so it moves in the opposite direction of the other. If you don't have a computer radio or just want to use one channel you can buy a reversing "Y" . This will reverse one servo. They usually come with an adjusting pot and cost about $17.

I used the mix on my Futaba 8UAF

snyder_man