I’m slightly disappointed by Lion’s iOS inspired feature to show a selection of accented characters on key hold.

On a German keyboard, when pressing <kbd>a</kbd>, I am able to choose between `ä`,  `â`, `à`, `á`, `æ`, `ã`, `å`, `ā`. So far so nice.

However, I feel some characters are missing. There is no `ç` (although I could type this one using <kbd>option</kbd>+<kbd>c</kbd>), no `ğ` and no `ł` either. On the other hand the letter `ń` is shown (which like `ł` is more or less only used in Polish) but to which OS X does not show an upper case version. <kbd>shift</kbd>+<kbd>n</kbd> yields no results.

Is there some way to enhance and expand this set of letters with own additions?