There's a reason why there's the old saying "don't shit where you eat." I'm constantly paranoid about punting in Hong Kong as I have far too many friends and relatives in this area, let alone worrying about the soap dilemma.
To be constructive though, an analysis of proposed solutions:
1) Rinse only without shower gel - Not too hygienic as water only doesn't kill germs.
2) Leave bottle of shower gel at regular - Limits punting selection only to regulars, but with most HG, they aren't in Hong Kong long enough. Also, I always fear what's left in the shower bottles are contaminated somehow.
3) Gym - Only if one is fit. Me, as a fat fuck, can't make use of this excuse.
4) Travel Pack - I know some brothers travel with a pack, including condoms, masks, extra sets of clothes and shower gels. I like this method the most.
My suggestion:
5) Develop a routine
But as another bro pointed out, men are inherently stinky. The best way to get undetected, and get to a 99.9% safety level is to develop a routine punting schedule. Schedule a dinner with friends at the Dai Pai Dongs that don't have air conditioning. Sweat out the cleanliness first. Make it a beer night as well so get some smoke on you. If you make every Wednesday of the week hanging out night, punt before that, and then spend 1-2 hours with your friends at dinner and bar. That'll cover up the smell, develop a stink on you which is explainable. I've been doing this for many years now (back when there were actually more Dai Pai Dongs in Hong Kong) and I'm still happily married.