I haven't ever seen one of those tunes so I'm not sure what they are doing but EFI systems do allow you to play with the fuel during decel. There is a menu in the Holley system for Decel Fuel Cutoff but I've never messed with it. I would imagine that you can do all sorts of things such as cut fuel off completely or continue to add small amounts. I'm sure those guys play with all the knobs to keep the cars up front.