Hi, guest Adam. The Ching Chung Chinaman expression is older than Monckton's "Geisha Girl" as well as "Chu Chin Chow." Lionel Monckton was producing musicals in the period 1898-1920. Moreover your words are a parody (unless it was some undocumented piece he did while at Oxford).

It has to be older than 1873 (Ching Chow Chung sheet music) and the 1880 ("The Chinee Laundryman" sheet music, with its chorus of Ching Chong opium).

I would like to find even older references, but it already seems certain that the expression started with the first Ching and Chong males who came to America.