Setting User-Agent in fetch tool

Hi, I am trying to update dynamic DNS (no-ip.com) and it seems that scripts that are flying around the net are not working because no-ip.com wants User-Agent set when making a http request. Does anyone know how one can achieve this with the fetch command? I do not seem to be able to find anything about this on wiki.

On the other hand, people use no-ip with Mikrotik, so there must be a way to update DNS records… :frowning:

Thanks in advance,