You do not need a straight line access, I use pull-pull on all my large models and many do NOT have a straight line to the servo. You can use nylon guide tubes well anchored where they touch structure, and do some amazing routing with no detriment to functionality. I have some large bipes that use this technique that are now 15+ years old with no problems in control on both elevator and rudder. Again, the secret for reliable operation is to have a slight amount of positive Ackerman built into the system and have the cables just snug enough at neutral to not have any sag. Now, straight line access is best and easiest if you can get it but is NOT MANDATORY.