This is one of our favorite rides! Maybe I might be able to help a little with some ideas.
There are ripped up fabric flags outside hanging all over by the entrance...that would look fun to drape across your letters. There are also lots of statues of Buhdda(??) and offerings under the statues. I think the theme is it's a worship place of monks or something. Not certain though...going from memory.
The inside cue is great! To wait in line is fun and it almost can move too fast because you want to read everything. The cue is almost like a museum about the Yeti. Does he really exist? Sighting articles, pictures, artifacts, footprints etc... So maybe you could do a small wanted style poster from the Old West cartridge with a typed up sign saying "Yeti sighting ahead" or something. You could also do a big giant footprint on your letter. The ride itself is themed that you are going on a backpacking trip/adventure into the Himalayan mountains and you encounter the Yeti. The ride goes backwards and forwards at top speeds so you could do some sort of sign post saying "fast speeds- beware".
Have you looked through the pictures of the ride yet? Try searching for images and it'll spark something I bet. I hope that gives you a few more ideas. You always come up with the most AMAZING stuff so I know you'll figure it out!