What you may have to do is run the throttle linkage against the fuselage side & angle the linkage across after the firewall.

99% of model engines don't have a spring return on the throttle. The cable Huck mentions has an inner cable & an outer sleeve & is quite stiff & will pull as well as push. I find cables, either wire type or plastic type (known as snakes or Gold N Rods), the easiest for throttle linkages. - John.