You can set these marks at the beginning of a source file with the !hyphen command for often used words. "Global" means that you only have to define the marks once.
If a word hasn't enough place at the end of a line when converting to ASCII, ST-Guide, Pure C Help or Manualpage UDO looks for a global definition in its internal list.
In the following example I expect that the word "documentation" is used many times in your source file:
!hyphen docu!-men!-ta!-tion