You may have already tried this, but I find that certain things in my diet make the smell worse. Also, is it possible that you are more sensitive to the smell than others? I'm guessing the other people will leave some smells too, because that's normal. They might even be worried about it themselves.
The thing that really works after the fact is lighting a match. If you leave the matches in there for everyone, perhaps others will use them as well and it will just be the thing that everyone does.
Another strategy I used when I had Ulcerative Colitis -- when I'd go in the morning, I'd turn the shower on first. Then go. Then use scented shampoo. That worked for both the smell and sound issues.
For what it's worth, I had a similar weekend experience sharing a bathroom with people I'd just met (when I had colitis and had urgency issues plus sound and smell issues) and it was surprisingly not stressful because everyone wasn't around all the time or paying attention to who was in the bathroom, etc. I was amazed at how much easier it was than I'd expected.
I hope you'll find it easier than you expect too!