Ok, I tried the squeeze technique this morning. Just to make sure I minimized variables, I started the car and let it idle for two minutes before engaging the transmission.
Indeed, gently squeezing the accelerator prevented any hesitation from showing up. This was similar to when I used my hand to depress the accelerator steadily while watching the rpm's: the rpm's immediately reacted to any pressure, with no perceptable play in the pedal mechanism, and no delay in the rpm increase.
Once I got out of the neighborhood and into more traffic, things were different. After pulling into a store to make a u-turn, as I was reentering the main street, I misjudged the speed of an oncoming van (which was obviously speeding on a Sunday morning). Having committed, I had no choice but to continue steadily squeezing the pedal, but I squeezed further to accelerate more quickly. That's where the hesitation became evident again. In fact, unless I'm mistaken, it felt like the power was going up, then something kept it down or brought it down, then as more time elapsed, the power slowly began to build and finally it really skyrocketed, but too late to avoid the other car having to slow down to avoid crashing into me (and of course he used his horn to let me know).
For some reason, the power delivery from a stop is non-linear, if you need more than minimal acceleration. I had the setting on Dynamic, by the way. The fact that it is so non-linear leads me to conclude that it's not simple turbo lag; I think it's engine-management related.
My difficulty starting the engine when it's been sitting for a few hours started when the dealer installed the two updates (060 and 043 rev. C). I'm thinking that may have something to do with this, but that's only a guess.
I guess I have to find time to leave it at the dealer again.
My Q4's thermometer read 87 degrees F when I first started it at 0800 hours this morning, by the way (housed in a hot garage). Outside temperature during my test was 79 degrees F. It's still warm here in the southwestern United States!