A fairly simple approach to testing if someone with the right equipment wants to take a run at it.
Eliminating the variables:
- Need to have identical pad wear
- Need to have identical placement
- Need to avoid reliance on human audio memory.
To deal with the above, I would suggest buying two of the same model headphones, building a jig that allowed for identical placement on the measurement rig, and two measurement rigs. Using the jig to place both headphones on the measurement rig on day 1 would ensure identical (within reasonable limits) placement and would ensure pad break-in would (within reasonable limits) to occur identically on both headphones. Take baseline measurements of both headphones
Play music/tones/whatever on headphone "A" for 30 days while leaving headphone "B" on it's rig without any input. Without moving the headphones, measure again on day 30.
While not perfect, I believe that process should show any non pad/placement changes due to burn in if any exist