All extended-*-{name,value}s? productions are designed to be recognized
as "token" by pre-2231 parsers. Following that thought through will
give you quite naturally the idea of where CFWS can occur.
furthermore the way I'd recommend implementing this is not by teaching the
parser to recognize 2231 parameters differently than ordinary MIME parameters,
but by parsing everything as MIME parameters. then the implementation can
look at the parameter names to see if there are any 2231 parameters there.
That's certainly how I implemented it.
Ned