Another different point-of-view: Delay may work for you, although it does not work well for me. I need predictable torque change on decel, and a delay causes the torque to randomly change after delay, perhaps into a turn or other maneuver where torque change part-way through is a bad thing. How I get around this on gear-change is simply to hold throttle steady, or perhaps lift throttle but not to completely closed, then punch the clutch in and out as quick as I can while throwing the gear, and back on the throttle again if I'm not still in it. The result is a much smoother power transition on shift (up or down), without DFC, but I have instant DFC when I go full decel.
This is a common shifting method in racing known as speed-shifting, and is easy to practice just driving to work at low throttle. I bet it will only take you a few minutes to get the feel of it, and it may become your new standard way to shift in any conditions. Personally, I prefer to hold whatever throttle I have in it, and usually do not lift at all. This works WOT or just cruising.
Finally, Speeduino has an optional shift feature (Flat-Shift) that holds whatever the rpm is when you engage the clutch, and can be very helpful tuning your speed-shift gear changes. Hope that helps.