Treat the simulacrum in the same way as you would treat a dominated version of the original.
That is - it should be plain with a sense motive that the creature is under a compulsion of some form, and his alignment will not change based on actions he is forced to do. Beyond that, on matters he isn't directly controlled on, he'll use his best judgement and behave according to his lawful-goodness.
I'd expect that creating a lawful-good character and then telling it "go kill so-and-so" would result in the simulacrum killing the target and then turning itself into the authorities, most likely spilling it's guts as to you and your whereabouts.
I'd guess the first command you give would be "Treat me as if I was your best friend, and the most important thing in the world to you". Even then a lawful-good sim would probably try to talk you out of your evil ways, or dob you in for your own good.