I often write comments within a method that refer to local variable names
within that method.  It would be nice if there was a switch to
automatically consider such variable names correctly spelled in those
comments.  

In my opinion that would actually decrease the risk of misspelling a
variable name in a comment (that is, writing something that is NOT a
variable name, believing that it IS a variable name) -- I don't use the
spell checker for variable names, so I don't get any warnings for variable
names themselves.