Well, with the cold, delayed spring and the epic rains of early/mid summer, here it is August 20 and I haven't tried any air layers.  Is it too late at this point?  I've heard recommendations that you should allow for 6-8 weeks of growing time -- would I be cutting it too close?
  Are there any techniques that would be better to use this late in the season -- i.e. maybe something that doesn't involve complete girdling of the limb just in case the air layer doesn't "take" in time?  Or is it not worth the risk?

A little late IMO unless we magically get hot in NJ. Airlayers work best when the tree is actively growing. I think our area is winding down. You could always make cuttings or wait till bud break next season. Spring to late spring is when I like to make airlayers although I put them on till the end of July in a normal summer.