I was annoyed at having to hatch multiple eggs to find a nature, so I figured this one out using a little trial and error:
Instant egg (replace XX to choose nature)
Well, it's not a complete solution. I noticed that the natures repeat in the same pattern on up (1a rash, 1b timid...), repeating over and over again. If you do the math, the a1 that was in the original code (which always gave naughty) is right where naughty should be in the 97-af range. I also tested 10 ralts, 5 adamant using 19, 5 adamant using 32. Most everything seemed random, stats, their best IV, but they all had syncronize, not one had trace as an ability.
So, that still needs to be figured out I think, but otherwise this works like a charm...