What version of LS are you working with? Prior to 6.7.2 there was a fixed set of tinymce parameters which could be changed.
Does anyone know TinyMCE configuration is picked up from which XML file and where the changes need to be done for further customization?
Have you tried searching the forums for this exact same question? Have you tried this thread: http://devnet.interwoven.com/forums_vb/showthread.php?t=30092&forumid=66