OK, one more go-round. I took the D90, 105 Micro AF-D and Gary Fong Puffer out on the dog walk (around a multi-acre meadow) this morning to field-test the proposal with whatever I could grab before I had to figure out where the dog had got to this time. I think it could work with a great deal less wind and more patience than I brought to the exercise. The insects were most uncooperative, skedaddling before I was anywhere near focus distance. Again I pre-set the focus of the 105 Micro to just the merest fraction of a turn before full extension (just short of 1:1). Focussing was accomplished with my legs and back muscles. The most patient bugs were grounded from wind. That made focussing and tripping the shutter too much like a video game for my taste. The two best exposures I was able to make involved still leaves in the shrubbery at the meadow's edge. Both were shot at 1/200, f40, iso 320, pop up flash (manual, full). Again, no crop, no PP other than LR's defaults, downsampling and the addition of LR's standard screen sharpening.
BTW, I make no claims for my abilities in this vein - it's not where my interests lie but, rather, I am intrigued by the question of reasonable flash enhancement while traveling light, hence the experiments. With practice it should be possible to learn to judge the correct plane to put the viewfinder focus on to achieve a reasonable DOF that extends from the nearest part of the beetle's wing cover to the tip of its far leg.
I think the real discovery involves the Puffer which eases the shadows and highlights immensely and helps avoid the harsh, flat look. Of course, at this scale, the position and size of the flash approximates an immense soft box positioned well above the camera at normal portrait distance. I made a few exposures of more static subjects (berries) which would definitely have benefitted from a tripod but indicate that the Puffer may actually be more valuable in this wise than the use for which it is marketed.