Is it possible to change the user-agent string used with Google Apps Script `UrlFetchApp.fetch` requests?

[This discussion](http://productforums.google.com/d/topic/apps-script/ejLKdBKHK24/discussion) from 2010 insinuates that the UrlFetch module in Google Apps Script supports adding the `User-Agent` header to the optional `headers` collection, like the UrlFetch module of Google App Engine does. However, [the GAS documentation](https://developers.google.com/apps-script/class_urlfetchapp) states nothing about this. A test script I made also shows it doesn't work.

Test script:

```
function testUserAgentString(){
  var page;
  try {
    page = UrlFetchApp.fetch('http://www.myuseragent.net/',
        {headers: {"User-Agent":
            "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6"
        }}).getContentText();
    Logger.log(page);
  } catch(_) {}
}

```

Log output (minus irrelevant HTML) was:

`Mozilla/5.0 (compatible; GoogleDocs; script; +http://docs.google.com)`

which is the default user-agent string used when doing UrlFetch requests by GAS.

Am I missing something or doing something wrong?

**Edit:** As this is currently not possible, I placed an enhancement [request](https://code.google.com/p/google-apps-script-issues/issues/detail?id=2544) on the Issue Tracker, per Arun's suggestion.