How to manualy tune the ATC_RAT_*_FF parameters in multicopters

The pages:

provide great resources for tuning multicopters, but I have not found any method nor step-by-step instructions on how to tune the ATC_RAT_*_FF parameters.
I’m hoping the the direct feed-forward will help me achieve better precision during vision-based precision landing.

Can someone help me out? I’m using Copter 4.0.4-rc3