Being clever would have taken time away from the goal of writing a book. It's arguable that the book would have been done sooner had they both taken the time to learn Morse Code (or Huffman Coding), but they quickly found a workable solution and got on with it.

They did one clever thing, though:

To make dictation more efficient, Bauby's interlocutor, Claude Mendibil, read from a special alphabet which consisted of the letters ordered in accordance with their frequency in the French language.