We've done well deep doing the following...
Using a T-series 350-400 grain, a cortland 325 grain or a Rio deep sea 350 grain etc - any line of this style, throw a modified clouser deep minnow tied with flashabou and chartruese highlights -or- a squid pattern -or- a herring pattern straight out to the side of the boat. As the boat drifts forward, allow the line to sink until it's angled off toward the rear of the boat and deep.
Retrieve slowly despite the natural tendency to rip it in for coho. Although you don't want to move it very far with each strip, jolt it pretty good to send out the signal pulse. Shock and stop. Let the boat drift move the fly for you in between jolts to keep it deep. Speed up the retrieve as the fly ascends toward the transom, tease any chasers by sight as the fly approaches the boat. Repeat.
Choosing the right drift is as important as anything else. Pick a seam where the coho are strafing bait and where the fly can be presented deep without falling to dogfish, ratfish, etc. I've done both on flies I am afraid to admit.
Unlike the random encounters of trolling, you need to seek out kelp beds on points where feeding activity is high on tide changes, large rocky outcroppings that break current up where fish can ambush bait, and work the slick lines where two major currents run alongside each other.
If you find krill, you'll find salmon. The herring gather around it and the salmon eat both the krill and the herring. My experience has been that you will also find horse mackeral around the krill, which are a kick on the fly rod but kind of anti-climatic after the initial hit.
Man I wish I could go there with you!