An other way is to use the attached bundle.
I wrote it some time ago. Simply press APPLE+SHIFT+O to invoke it. You can browse for a file, set the file's encoding, the output format, etc. You can edit icf.plist to add more encodings. The whole bundle is working with 'iconv' and 'textutil' - see man pages for more details.
You also can drag&drop a file from the Finder to an empty TM window. This also will invoke that dialog.
Cheers,
Hans