how to set a fill suffix?

Question

I want to fill (wrap) long lines at n characters, ensuring that each new line ends with "///". (That is the "continuation character" for long lines in Stata code.

So that something like this

This is a long line. This is a long line. This is a long line. This is a long line. This is a long line. This is a long line.

would be broken up into something like this

This is a long line. This is a long line. This is a long line. This ///
  is a long line. This is a long line. This is a long line.

(where the first line, along with the /// is no more than n characters.

I see info about prefixes in the fill section of the manual, but nothing about suffixes.

Thanks!