I've just made a realy quick and dirty bookmarklet. It's only tested in firefox 2 and it's not quite how I would like it to work but it's a start. I'll hopefully update it later to work better.
Just add the following URL as a bookmark:
javascript:(function(){var d=document;var b=d.body;var c=b.insertBefore(d.createElement('center'),b.firstChild); var dv=c.appendChild(d.createElement('iframe'));dv.id='ifrm'; dv.height='30%';dv.width='100%';dv.src='http://news.ycombinator.com/submit'; d.getElementById('ifrm').scrollIntoView(); })();
Let me know if it works.