Install HN Toolkit and enable split view in the options.

For Firefox (+ Greasemonkey): http://userscripts.org/scripts/show/25039

For Chromium: http://gist.github.com/355697 (click the 'raw' link)

Is it possible to hijack the 'middle click' on a link so that it opens the split view in a new tab?

I don't think it can be done by capturing the middle click, but you could achieve the same effect by changing the script such that the HN submission ID is added as a url fragment id or dummy URL param to the submission link. Then another script can be used to check the referrer property of each page loaded, and if it points to HN you could insert an iframe and open the comments link using the submission id in the url.

Why not hack it together yourself? ;)

Parse the rss feed and pull in the url in an iframe and the comments page in one. Give them both a height/width of 50% and voila.

As a lazy programmer I wanted to find out if anyone had done something about it. It's a fairly obvious itch that I'm pretty sure someone must have scratched it already. ;)

Maybe this one - http://userscripts.org/scripts/show/30512 ?

it would be great if this could open a new tab with the split views on 'middle click' instead opening all links in the same page