Actually there was a case in 2012 of someone tried under this law for having fisting videos. They weren't convicted. This is strong evidence (and precedent) that fisting per se would not fall under this law.
That it even made it to court meant there was a case to answer but the actual outcomes seem to be more sane and based on the context than the law itself.
I believe the crux was that the law said it was illegal to have porn that showed damage to the anus, so does fisting fall into that category or not? The outcome was no, fisting doesn't count as damage to the anus. The "stupid law" wasn't ignored, it wasn't a case of "people using their own moral compasses", it was a jury & judge interpreting a law, like normal.
That it even made it to court meant there was a case to answer
The cynic is me notices that the accused was a lawyer who helped prosecute corrupt police officers.
I'm no lawyer, but it already is, if they're in a pornographic "context": http://en.wikipedia.org/wiki/Section_63_of_the_Criminal_Just...
This 2008 act outlaws possessing or publishing explicit and realistic imagery of acts that threaten life, would cause serious injury to certain genitals, etc.
So fisting, simulated murder, or simulated necrophilia.. already illegal. Rape, borderline allowable, although if I were a lawyer testing this act in court, I'd say that rape is quite clearly an act that is "likely to result" in "serious injury to a person's anus, breasts or genitals".