My KO additions really are KO additions, with aroma and flavor being their entire point.
The KO addition goes in, power is cut to the elements, the wort stands for about 1min while I apply plastic wrap to the top of the kettle and around the immersion chiller's neck, then the chiller is turned on full bore and the whirlpool valves are re-opened. WIthin 3-4mins the top of the wort is below 170F/76C and isomerization ceases.
You're correct in assuming that there is IBU creep, but I will suggest that it is negligible--and, after 30 years of brewing, I'm quite certain that I have a better feel for that hop creep than the dubious algorithms used by software. As a Beersmith user, I think the application ascribes far, far too many IBUs to whirlpool additions. But I write that knowing that my rig is optimized to crash quickly. Mr. Smith has to guestimate everyone's chilling efficiency, and that's no easy task!