Anderson's needle through arm illusion IS an illusion... it uses the latex method described previously in this thread.
And in fact, I've yet to find any reference to the string in stomach illusion which actually involves breaking the skin, although I've found countless mentions of the latex pocket version.
The only man who can really solve this argument is Yankee Tom, as he's the man when it comes to prosthetics.
YT or someone else may even know Cornelius Gold of the Blood Brothers - who performs a very gory 'string from stomach' routine... and I'd be willing to bet there's no penetrations (although he'd probably not reveal his method anyway!)
And like Mandrake says... DON'T TRY THIS AT HOME... even with a sterile needle.
I don't know if any of you guys are familiar with Jackass or Dirty Sanchez, but I would imagine even those crazy dudes would laugh in your face if you suggested the 'threading half a foot of sterile thread with a sterile needle from below the belt line into your midrift, and pulling the thread out of your belly' routine.
Like we've said, we're magicians, not surgeons! There's an art to illusion, whereas there's no art to self-mutilation (although I'm sure anybody with piercings on their person will disagree

- but I think you know what I'm talking about)