Possible Clues:

• Men spy duo concocting alias
• George Eliot, say, used pony oddly at start of Middlemarch
• Crossword compiler might need this work out -- one's dumpy
• Used pony to travel with Mike (not his real name)
• Mark Twain or Elena Ferrante, e.g.
• E. Pound's my new pen name!
• Author's name Dumpynose perhaps
• £25 includes charges for returning minute new handle?
• Afterthought proper to turn up on my return, having assumed title
• Author's other name