Hi seamuschimp,
I'm having a hard time trying to define manipulated unnaturally as all zoos are guilty of it by simply putting animals in a captive environment.
Anyways, now is considered a "down time" for shows at Singapore Zoo as 2 out of the 4 shows are currently suspended for upgrading of amphitheatres. The 2 that are on now are "Elephants at Work and Play" and "Splash Safari".
Elephants at Work and Play should be avoided if you are sensitive to the Asian-style of handling elephants. The ankus is used minimally, and the "tricks" are unnatural to a large extent (hauling, lifting logs, trunk waves, salutes...).
Splash Safari is the typical "sea world" type of show with Californian Sealions jumping out of the water, hitting ball targets, catching frisbees and such.
I've seen many visitors who are morally opposed to animal shows still enjoy the other animal exhibits at the Zoo. They simply avoid the shows.
Hope this answers your questions. Cheers