I've fished the American side with a two hander several times with not much success. I used a 15' Winston DBF 9wt with a modified Mastery Spey that had 12 feet of LC-13 on the end and a weighted bunny spey. I call it my "get down" line. Casting it isn't as gruesome as you'd think, the DBF just starts to load once I tacked the LC-13 on to it. Plain 'ol double spey's just fine as long as the fly and tip up and "buzzing" on the suface, as Derek Brown would say.
This issue really isn't the casts as much as the currents. The only really decent swinging currents I've found are just above and below Devils Hole. There's spot just above that the gear fishermen do well with, but there is no back cast room at all as you're standing on rocks. If the water is low and not pouring into the hole you can try the upper outer edges with overhead casts. I've had a few follow bunny speys and such up to the top while stipping. No takers, just surprised blank stares on both sides. The problem here is that if you hook one of those lower river hogs he's either blowing out into the heavy current and taking your line, or, if you get past that point in the fight, you have some pretty dicey landing areas. Whatever you do near the Hole keep an eye to the shore. If they start releasing water below it comes up very fast.
I know a few folks who have successfully fished the Artpark (above) drift with bunny speys and zonkers. You might try there. Because the back of the gorge is one or two steps from 20 feet of fast flow you'll have to angle upriver with your casts or have your fly blow right past the fish to shore. My attempts were really to get down ASAP and swing slowly to shore. The fish are not far out, but they do hold against a sharp drop. It's my understanding that they hold off the drop and that the gear fishermen are indeed getting pretty far down (at least on that side).
I wanted to take a Scandanavian rig down there this year but I think I'm holding out until spring to make the trip. That all said, sounds like your buddy knows where the fish are and may just need a new delivery device and change in technique. If I had it to do over I'd start down there with something like a Scandanavian or Skagit style rig.
BTW - Take care down there. As you know it's dangerous and can get icy slick in the winter, especially above the Hole.