Notepad++ gives no options for built-in language lexers. They are in fact part of underlying Scintilla project.
So, if you are not keen enough to change built-in lexer by yourself, then the answer for you is there is no way. Otherwise find your lexer in scintilla\lexers\
folder in N++ source package and start playing with it. (And if you find solution to effectively solve the problem with /***/
, you might consider contributing it back to Scintilla project.) Third option is to chcek Scintilla Bug tracker and if this problem is not reported already, you can create a new bug report.