I have experienced it!
I asked the same question in the HK post, but with no answer, I think we have to try.
I know someone around who did put pads' pieces in the big hole to plant olive
trees.
I do mulch and will take pics of my fig tree with "tunera".
I have big humps, that could not rot, as the rain never came, so they produce a lot of little pads, that we have to cut again...
And I have started to bury some, in little bits.
Interesting info: you get as much
carbon with opuntia than with wheat
straw
...but with 3 times less water to produce it!
So I keep my opuntia
roots as much as possible, and will harvest them for carbon.