I have used this method in similar situations where the carb arm is metal. It might be OK on a plastic arm but I have not tried it..

Take a 1 inch bolt that fits the hole in the throttle arm. Take a ball end pushrod and fit the ball up against the head with a nut. Use two nuts and fit the bolt to the throttle arm. Use Locktite.

If needs be the plastic part that screws onto the rod can be shortened to as little as 1/4 inch and still have a good grip.

This gives you a 7/8ths inch offset from the throttle which is enough to get a direct link from the servo to the thottle.