All we did was record a journal file which does this for us. Go to tools --> journal __> record. Then go through the steps to create this snapshot. During our part release we make stp files, PDF files, and do a couple other things. So at the end of our Release script we have the following snip bits of code. This works well for us. I am not a coder I am code novice. (I would like to better in this area) So maybe someone else could get you a complete code to do what you are wanting. I would like to note we open our drawings in NX and release our drawings and then submit them to a work flow in teamcenter to release the drawing. So this code is ran NX. If you do not open the drawing before you submit to a workflow you will need to set a standard of when you run your automatic snapshot journal.
End If Next workPart.DrawingCompare.CreateSnapshot() Next