I don't do it... but I can tell you that for the purposes of IBU calculations, treat it like it's in the boil the whole time... because it is, and photospectroscopy proves that FWH gives your more IBUs than regular boil additions. Tasting experiments have been all over the board as to how bitter it actually tastes. Everyone refers to the old one from like 50 years ago where the FWH resulted in "smoother" bitterness. However the experiments I've read about more recently couldn't tell much difference between FWH and a regular 60-minute addition. Which makes perfect sense to me. If you want to try FWH, consider doing an experiment with two batches in one day using different hopping techniques, and please report back your experience.