Converting .xls to google spreadsheet in google apps script

I have an .xls file stored in Google Drive. I want to convert it to the Google Sheets spreadsheet file format from Google Apps Script. Is there any way to do this without external solutions?

This is now possible using the Advanced Drive service:

https://developers.google.com/apps-script/advanced/drive

When using Drive.Files.insert, simply set the optional parameter "convert" to "true".

var file = {
    title: 'Converted Spreadsheet'
  };
  file = Drive.Files.insert(file, xlsxBlob, {
    convert: true
  });

This was also obtained from the above given issue

Other than using the delivered 'upload' and convert functions, it's not currently available. Requesting enhancement request here: http://code.google.com/p/google-apps-script-issues/issues/detail?id=1019

Here's the complete code to create a file in a particular folder: (was a hint but was not completely apparent to me from @ben-visness comment)

var file = { 
    "title": filename, 
    "parents": [{"id": folderId}]
};
file = Drive.Files.insert(file, blobObj, {
    "convert": true
});

Note: This will require enabling advanced Drive service from within Google Apps Script - Menu > Resources > Advanced Google Services AND Menu > Resources > Advanced Google Services > Google API Console.