On a Catalins 27 the outhaul is rigged internally and the control line exits the boom about midway and runs to a clam cleat with a fairlead a foot or so farther back. You want located mid boom so it's still reachable when the boom is swung out beyond the cockpit. You can rig the control line to go all the way to the mast, then back to a cleat near the cockpit. However, it may will create more friction, especially since it appears your outhaul is externally rigged with significant purchase in a multiple block set up. If you want to reduce the friction, I suggest going with a smaller diameter line, certainly no larger than 1/4". You can even use a very small diameter single braid dyneema, like 3/16 or 1/8 Samson Amsteel, then cover the part that's cleated with a Dacron sheath for better handling and cleating. The outside cover of any Dacron double braid would suffice. size would be 2/16 larger than dyneema core. I know this explanation sounds bizarre and complicated, but trust me, an outhaul with a lot of friction.. from the foot of the sail and the complexity and bulkiness of the control system.... will not work well and you'll get tired of messing with it.
Most outhauls employ the small diameter hi tech line or wire rope for exactly that reason.