Spell a message in a sudoku puzzle

A programme that writes any message into a working sudoku puzzle, providing it contains at most 9 distict characters with no more than 9 of each.

The letters making up the message appear in order and are highlighted, since more cells generally have to be filled in to give a unique solution to the puzzle. There is a lot of randomisation in the puzzle generation, so you can keep generating puzzles until you see one you like the look of.