Well I can't stop anyone from wanting to call any other some one by some name
But just for some info from a chinese perspective (I'm a Singaporean Chinese by the way):
1) Normally when the Chinese call someone with the additional "er" to their name, it means that someone is either a child or very dear to them (sweetheart, wife). "Er" in chinese actually means "child" by the way.
2) When we add "er" we add it to the given name and not the family name/surname. Zhang Anda - "Zhang" is the family name/surname (or last name to the Westerners), and "An" and "Da" are the given names.
3) So if you want to address him in the Chinese way, it should be "An-er" or "Da-er" (More appropriately "Da-er", as it is the last word to the chinese name), never "Zhang-er"
BUT well... you need not be right on this island... you just need snooker
*NOTE* - An interesting result if you apply this to the western name...
Mark = Mark-er
... Any other interesting name you can think of?