Well let's look at what a star does when it twinkles. Basically thermal cells in the atmosphere (about 2KM across) refract the light from the star causing it to appear to be in a slightly different place in the sky. As the star is a point source this movement looks to be outside the visible disc. So in effect the star "dances" around a nominal point in the sky in a random none periodic way.
So to simulate this exactly is tricky because the LED is not a point source and in general you can't move it. So I would guess you would be reduced to having it on most of the time and to have it blink off at random intervals. I think the trick might be getting the random range sorted both for time between blinks and off time during the blink.