Just get it close, if it's a 2 stroke then there's enough distance between the firewall and the carb that the pushrod will flex. I would pay more attention to where the sheath exits in the radio compartment, you want it as direct a route to the throttle servo as you can. Like Minn says, you can always bend the pushrod going to the throttle, but bending the pushrod in the radio compartment may make it difficult to remove/install the fuel tank.
I've always had good luck using Du-Bro throttle cables, just make sure you tin the ends so it won't fray and stays stiffer.

Andy