Bruder dozer servo help

[komatsu97]

Evening all,
I have converted a Bruder D5 Dozer, using a sabertooth controller and an old rc plane transmitter. I used the elevator and rudder stick for directional control, and the throttle for the blade control so I can hold a desired height of the blade easily, as it is not spring centered. I have decided to use a servo to angle the blade controlled by the aileron channel (left and right on the throttle stick). the question I have is how to stop the servo from self centering, for example; Angle the blade to the left, and let the stick spring return to center, but the blade stays in that position until i move the stick again.

Any advice would be appreciated

Cheers,
Liam