Here's a trick for targeting Wahoo on flies. They'll come across a trolling spread and either cut off a couple of lures or get hooked. Immediately after recognizing this, stop the boat and cast into the wake. Let the fly dead-drift. The fish hunts by maiming its' prey and doubling back to eat, so chaces are they'll double back and find the fly.
If the boat's moved past the initial strike zone, or the fly guy is not ready, throw something overboard to mark the spot turn the boat around ASAP, and try to dump the fly as close to the initial strike as possible. One generally has a couple of minutes while the fish are searching for bits of whatewver they just attacked.
I've never tried this locally, since they are so rare around here, but routiunely have a wire-tippet rod ready when fishing the Pacific or Carribean.