If written well, Jaimie explaining why he killed his father to Dany would be a very nice scene. I think he ever only told Brienne, and never cared about explaining himself with other people, but maybe he would do Dany the courtesy of telling her exactly why.
I'm not so sure however if Jaimie can be turned against Cersei with logic. By now, once we crossed off the R+L=J thing from the list of theories into the list of known facts, the most popular theory is Jaimie killing Cersei, and I expect it to be a desperate spur of the moment thing like it happened with the Mad King.