So since we're doing the question game, couldn't running a colder plug in this case work instead of adding a shim? Maybe some of the engine gurus can answer.
Having done my research I have gathered the following:
Adding NItro = Advance Timing
Adding Shim = Retard Timing
Colder Plug = Retard Timing

Since you're adding nitro the timing is advanced. You want to add the shim to bring back the timing. But wouldn't the colder plug do the same? Adding a shim, will reduce compression which should reduce power. Why would we want to do that?

Just random thoughts and questions that run through my mind, thought maybe I should throw them out there and see what others think. So rant away