If I recall correctly, on the C64 all you need to do it enable the magic switch: 'poke 53280,5' and then create a loop for sampling...
From the top of my head:
10 poke 53280,5 (that's the important part)
20 for i=0 to 100
30 print i
40 goto 20
That should do it. Also, it's really fast.
On a serious note, I'm still a bit puzzled that all the 'caustics don't work' talk is based on a picture of a golden Jesus statue in a pool.