I was just on Jungle Cruise earlier this week, and as you've said, it was practically walk-on. So far I've circled the jungle five times, and only once was the skipper a little lacking on performance. The rest were fabulous as always, still acting like they are telling the jokes for the first time, rather than the 10,001st time.
I think people overlook Jungle Cruise because they don't buy into the humor. I always give a huge round of applause for... THE BACK SIDE OF WATER YEAH WOOHOO!
Thats just an example of the enthusiasm which you can use to assist the skipper in creating the atmosphere. I also try to laugh outloud when the fellow crew are silent/not in the mood to laugh. That reminds me, I was with a bunch of people who just would not smile or laugh at any of the jokes. It was surreal! Why the heck would you ride Jungle Cruise if you're just going to sit there and look grumpy? Jungle Cruise might be the absolute worst ride for grumpy people.