Any chance we could add decodeEncryptedAddressFromPrivateKey( key ) {}? I'll spare you a few lines:

function(key, pass) {
    if(key[0] == '6') {
      var eckey = Bitcoin.ECKey.decodeEncryptedFormat(key,pass);
      return Bitcoin.Util.bytesToHex(key.getPrivateKeyByteArray());
    }
    else return 'not an encrypted key'
}