If you don't want to bother with 1/2 dozen drain refills, stick with the cooler line flush. But, you'll still need to do a drain/refill prior to starting.
Disconnect either ATF cooler line hose. Attach some hose to the disconnected ATF fitting(purchased from the local hardware store--3/8, 5/16, or 11/32" hose). Aim both hoses into the bucket. When you start the vehicle, your ATF will flow out of 1 of the hoses. Do the flush and label the ATF flow with a paint pen for future flushes(not needed if you practice the simple yearly drain/refill once or twice a year).
Also, if there is ATF flow in P or N, there is no need to have your helper put the tranny in D.