[ESS] add a keyword to font-lock-keywords

[BBS Querschnittsprojekt: Gerhard Schön]

Dear All,

in stata, you can comment a line with "//".
How can I add the keyword "//" to the keyword list, 
that font locking will work like in /* ... */  or
like ";" in lisp?
Actually, ESS don't highlight "//" as a comment line 
in (ESS[STA]) - mode.

Thanks in advance,
Gerhard