Im not a fan of theories but this popped into my cranium so im posting it.

I figure the same way sasuke only had to see his bro die to get his MS
(cuz we all know sasuke didnt kill itachi) Kakashi might've gotten his MS just by seeing obito or rin die and he never tried it out till shippuden. Im really not seeing any other ways as to how he got his MS, dammit tell us Kishi