I think that Lee Tung Fu would have made an interesting partner for Charlie Chan. As Kashimo, I don't know, though, as Kashimo's frenetic nature would not, I feel, have been suited to the more reserved demenor of Lee Tung Fu. I think that an original character could have been created, instead. Perhaps he could have played a more traditional cousin who wasn't pleased with his cousin Charlie Chan and his family having become so westernized! (I believe that in one of the Biggers books that some cousin actually did have such qualms.)
What I meant was how he would have interpreted the same role, same dialogue with his own mannerisms. It always fascinates me how different actors can give different meanings to the same role.